fix(model): avoid unhandled error if createIndex() throws a sync error

Author: vkarpov15

lib/model.js

@@ -1653,7 +1653,24 @@ function _ensureIndexes(model, options, callback) {
       }
     }
 
-    model.collection.createIndex(indexFields, indexOptions).then(
+    // Just in case `createIndex()` throws a sync error
+    let promise = null;
+    try {
+      promise = model.collection.createIndex(indexFields, indexOptions);
+    } catch (err) {
+      if (!indexError) {
+        indexError = err;
+      }
+      if (!model.$caught) {
+        model.emit('error', err);
+      }
+
+      indexSingleDone(err, indexFields, indexOptions);
+      create();
+      return;
+    }
+
+    promise.then(
       name => {
         indexSingleDone(null, indexFields, indexOptions, name);
         create();