Optimize UI code

Source/Engine/UI/GUI/Control.cs

@@ -122,8 +122,6 @@ namespace FlaxEngine.GUI
                 if (_parent == value)
                     return;
 
-                Defocus();
-
                 Float2 oldParentSize;
                 if (_parent != null)
                 {

Source/Engine/UI/UICanvas.cpp

@@ -23,11 +23,11 @@ MMethod* UICanvas_EndPlay = nullptr;
 MMethod* UICanvas_ParentChanged = nullptr;
 
 #define UICANVAS_INVOKE(event) \
-    auto instance = GetManagedInstance(); \
-    if (instance) \
+    auto* managed = GetManagedInstance(); \
+    if (managed) \
     { \
 	    MObject* exception = nullptr; \
-	    UICanvas_##event->Invoke(instance, nullptr, &exception); \
+	    UICanvas_##event->Invoke(managed, nullptr, &exception); \
 	    if (exception) \
 	    { \
 		    MException ex(exception); \

Source/Engine/UI/UIControl.cpp

@@ -22,10 +22,11 @@ MMethod* UIControl_BeginPlay = nullptr;
 MMethod* UIControl_EndPlay = nullptr;
 
 #define UICONTROL_INVOKE(event) \
-	if (HasManagedInstance()) \
+    auto* managed = GetManagedInstance(); \
+    if (managed) \
 	{ \
 	    MObject* exception = nullptr; \
-	    UIControl_##event->Invoke(GetManagedInstance(), nullptr, &exception); \
+	    UIControl_##event->Invoke(managed, nullptr, &exception); \
 	    if (exception) \
 	    { \
 		    MException ex(exception); \