Fix memory leak when calling instanceof on QML items

The return value of getType() has the ref count increased and needs
handling on the caller side.

Change-Id: I05ffa4dae221f2502f87b76762164bba1389db32
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/qml/qml/qqmltypewrapper.cpp

@@ -388,6 +388,7 @@ ReturnedValue QQmlTypeWrapper::instanceOf(const Object *typeObject, const Value
         QQmlTypeData *td = qenginepriv->typeLoader.getType(typeWrapper->d()->type().sourceUrl());
         CompiledData::CompilationUnit *cu = td->compilationUnit();
         myQmlType = qenginepriv->metaObjectForType(cu->metaTypeId);
+        td->release();
     } else {
         myQmlType = qenginepriv->metaObjectForType(myTypeId);
     }