QtQml: Construct return type before metaCall

The metacall expects initialized memory. Let's give it what it wants.

Fixes: QTBUG-117672
Change-Id: If139029ac4771ac919c5f09728633546e7bb9d1e
Reviewed-by: Olivier De Cannière <olivier.decanniere@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qml/jsruntime/qv4jscall_p.h

@@ -485,6 +485,8 @@ void coerceAndCall(
         } else if (returnType.sizeOf() > 0) {
             Q_ALLOCA_ASSIGN(void, transformedResult, returnType.sizeOf());
             transformedArguments[0] = transformedResult;
+            if (returnType.flags() & QMetaType::NeedsConstruction)
+                returnType.construct(transformedResult);
         } else {
             transformedResult = transformedArguments[0] = &argc; // Some non-null marker value
         }