Use a strong NSError when returning from methods with nested autoreleasepool

Otherwise, the output NSError arg get assigned an autoreleasing NSError object that gets deallocated when the nested autorelease pool is drained and no error is reported

Author: shoumikhin

backends/apple/coreml/runtime/delegate/ETCoreMLModelManager.mm

@@ -728,6 +728,8 @@ - (BOOL)executeModelWithHandle:(ModelHandle *)handle
                                       args.count);
         return NO;
     }
+    NSError *localError = nil;
+    NSArray<MLMultiArray *> *modelOutputs = nil;
     @autoreleasepool {
         NSArray<MLMultiArray *> *inputs = [args subarrayWithRange:NSMakeRange(0, model.orderedInputNames.count)];
         NSArray<MLMultiArray *> *outputs = [args subarrayWithRange:NSMakeRange(model.orderedInputNames.count, args.count - model.orderedInputNames.count)];
@@ -736,19 +738,22 @@ - (BOOL)executeModelWithHandle:(ModelHandle *)handle
             outputBackings = outputs;
         }
 
-        NSArray<MLMultiArray *> *modelOutputs = [self executeModelUsingExecutor:executor
-                                                                         inputs:inputs
-                                                                 outputBackings:outputBackings
-                                                                 loggingOptions:loggingOptions
-                                                                    eventLogger:eventLogger
-                                                                          error:error];
-        if (!modelOutputs) {
-            return NO;
+        modelOutputs = [self executeModelUsingExecutor:executor
+                                                inputs:inputs
+                                        outputBackings:outputBackings
+                                        loggingOptions:loggingOptions
+                                           eventLogger:eventLogger
+                                                 error:error];
+        if (modelOutputs) {
+            ::set_outputs(outputs, modelOutputs);
         }
-        
-        ::set_outputs(outputs, modelOutputs);
     }
-    
+    if (!modelOutputs) {
+        if (error) {
+            *error = localError;
+        }
+        return NO;
+    }
     return YES;
 }
 
@@ -777,40 +782,41 @@ - (BOOL)executeModelWithHandle:(ModelHandle *)handle
 
     std::vector<executorchcoreml::MultiArray> inputArgs(argsVec.begin(), argsVec.begin() + model.orderedInputNames.count);
     std::vector<executorchcoreml::MultiArray> outputArgs(argsVec.begin() + model.orderedInputNames.count, argsVec.end());
+    NSError *localError = nil;
+    NSArray<MLMultiArray *> *modelOutputs = nil;
     @autoreleasepool {
         NSArray<MLMultiArray *> *inputs = [model prepareInputs:inputArgs error:error];
-        if (!inputs) {
-            return NO;
-        }
-        
-        NSArray<MLMultiArray *> *outputBackings = @[];
-        if (executor.ignoreOutputBackings == NO) {
-            outputBackings = [model prepareOutputBackings:outputArgs error:error];
-        }
-        
-        if (!outputBackings) {
-            return NO;
-        }
-        
-        NSArray<MLMultiArray *> *modelOutputs = [self executeModelUsingExecutor:executor
-                                                                         inputs:inputs
-                                                                 outputBackings:outputBackings
-                                                                 loggingOptions:loggingOptions
-                                                                    eventLogger:eventLogger
-                                                                          error:error];
-        if (!modelOutputs) {
-            return NO;
+        if (inputs) {
+            NSArray<MLMultiArray *> *outputBackings = @[];
+            if (executor.ignoreOutputBackings == NO) {
+                outputBackings = [model prepareOutputBackings:outputArgs error:error];
+            }
+            if (outputBackings) {
+                modelOutputs = [self executeModelUsingExecutor:executor
+                                                        inputs:inputs
+                                                outputBackings:outputBackings
+                                                loggingOptions:loggingOptions
+                                                   eventLogger:eventLogger
+                                                         error:error];
+                if (!modelOutputs) {
+                    // Resize for dynamic shapes
+                    for (int i = 0; i < outputArgs.size(); i++) {
+                        auto new_size = to_vector<size_t>(modelOutputs[i].shape);
+                        outputArgs[i].resize(new_size);
+                        argsVec[model.orderedInputNames.count + i].resize(new_size);
+                    }
+                    ::set_outputs(outputArgs, modelOutputs);
+                }
+            }
         }
-        
-        // Resize for dynamic shapes
-        for (int i = 0; i < outputArgs.size(); i++) {
-            auto new_size = to_vector<size_t>(modelOutputs[i].shape);
-            outputArgs[i].resize(new_size);
-            argsVec[model.orderedInputNames.count + i].resize(new_size);
+    }
+    if (!modelOutputs) {
+        if (error) {
+            *error = localError;
         }
-        ::set_outputs(outputArgs, modelOutputs);
-        return YES;
+        return NO;
     }
+    return YES;
 }
 
 - (BOOL)unloadModelWithHandle:(ModelHandle *)handle {