Fix undefined behavior in model.h.

The function LiteRtTensorT::NumElements() was assuming that
decltype(dims[0])=`const int` if dims is a const reference to an array
of ints. In fact, it's `const int&`. The effect is a difference in
behavior between optimized and non-optimized builds.

LiteRT-PiperOrigin-RevId: 819888199

Author: ai-edge-bot

litert/core/model/model.h

@@ -25,6 +25,7 @@
 #include <numeric>
 #include <optional>
 #include <string>
+#include <type_traits>
 #include <unordered_map>
 #include <utility>
 #include <variant>
@@ -389,9 +390,9 @@ class LiteRtTensorT {
       return 0;
     }
     const auto& dims = ranked->layout.dimensions;
-    return static_cast<size_t>(
-        std::accumulate(std::cbegin(dims), std::cend(dims), 1,
-                        std::multiplies<decltype(dims[0])>()));
+    return static_cast<size_t>(std::accumulate(
+        std::cbegin(dims), std::cend(dims), 1,
+        std::multiplies<std::remove_reference_t<decltype(dims[0])>>()));
   }
 
   // Set the tensor type.

litert/core/model/model_test.cc

@@ -166,6 +166,7 @@ TEST(ModelSubgraphTest, Input) {
   LiteRtSubgraphT subgraph;
   subgraph.Inputs().push_back(&tensor);
   EXPECT_EQ(&subgraph.Input(0), subgraph.Inputs().front());
+  EXPECT_EQ(tensor.NumElements(), 0);
 }
 
 TEST(ModelSubgraphTest, Output) {