Defer the render plugin reinit to main thread (#1626)

Fix a problem with reloading actor in emfx studio crashes the editor 
Signed-off-by: rhhong <rhhong@amazon.com>

Gems/EMotionFX/Code/EMotionFX/Pipeline/SceneAPIExt/Behaviors/ActorGroupBehavior.cpp

@@ -168,7 +168,7 @@ namespace EMotionFX
 
             AZ::SceneAPI::Events::ProcessingResult ActorGroupBehavior::BuildDefault(AZ::SceneAPI::Containers::Scene& scene) const
             {
-                // Skip adding the actor group if it's already exist.
+                // Skip adding the actor group if it already exists.
                 if (SceneHasActorGroup(scene))
                 {
                     return AZ::SceneAPI::Events::ProcessingResult::Ignored;
@@ -185,7 +185,7 @@ namespace EMotionFX
                 }
                 
                 const bool hasAnimationData = AZ::SceneAPI::Utilities::DoesSceneGraphContainDataLike<AZ::SceneAPI::DataTypes::IAnimationData>(scene, true);
-                // Skip adding the actor group if it's contain animation data but don't contain any skindata or blendshapedata.
+                // Skip adding the actor group if it contains animation data but doesn't contain any skin or blendshape data.
                 if (hasAnimationData && !hasSkinData && !hasBlendShapeData)
                 {
                     return AZ::SceneAPI::Events::ProcessingResult::Ignored;

Gems/EMotionFX/Code/EMotionFX/Tools/EMotionStudio/EMStudioSDK/Source/RenderPlugin/RenderPlugin.cpp

@@ -313,7 +313,7 @@ namespace EMStudio
 
     void RenderPlugin::OnActorReady([[maybe_unused]] EMotionFX::Actor* actor)
     {
-        ReInit(/*resetViewCloseup=*/true);
+        m_reinitRequested = true;
     }
 
     // try to locate the helper actor for a given instance
@@ -535,6 +535,7 @@ namespace EMStudio
         }
 
         mFirstFrameAfterReInit = true;
+        m_reinitRequested = false;
 
         // zoom the camera to the available character only in case we're dealing with a single instance
         if (resetViewCloseup && numActorInstances == 1)
@@ -851,6 +852,11 @@ namespace EMStudio
             return;
         }
 
+        if (m_reinitRequested)
+        {
+            ReInit(/*resetViewCloseup=*/true);
+        }
+
         // update EMotion FX, but don't render
         UpdateActorInstances(timePassedInSeconds);
 

Gems/EMotionFX/Code/EMotionFX/Tools/EMotionStudio/EMStudioSDK/Source/RenderPlugin/RenderPlugin.h

@@ -226,6 +226,7 @@ namespace EMStudio
         QWidget*                            mInnerWidget;
         CommandSystem::SelectionList*       mCurrentSelection;
         bool                                mFirstFrameAfterReInit;
+        bool                                m_reinitRequested = false;
 
         // command callbacks
         MCORE_DEFINECOMMANDCALLBACK(UpdateRenderActorsCallback);