Fix variious issues

Source/Editor/Modules/UIModule.cs

@@ -447,6 +447,8 @@ namespace FlaxEditor.Modules
 
         private void StateMachineOnStateChanged()
         {
+            if (Editor.StateMachine.CurrentState is States.ClosingState)
+                return;
             UpdateToolstrip();
             UpdateStatusBar();
         }

Source/Editor/Windows/GameCookerWindow.cs

@@ -648,7 +648,7 @@ namespace FlaxEditor.Windows
         /// <returns>True if can build, otherwise false.</returns>
         public bool CanBuild(PlatformType platformType)
         {
-            if (_buildTabProxy.PerPlatformOptions.TryGetValue(platformType, out var platform))
+            if (_buildTabProxy != null && _buildTabProxy.PerPlatformOptions.TryGetValue(platformType, out var platform))
                 return platform.IsAvailable && platform.IsSupported;
             return false;
         }

Source/Engine/Core/Math/Quaternion.h

@@ -393,8 +393,8 @@ public:
     /// <returns>The inverse of the specified quaternion.</returns>
     static Quaternion Invert(const Quaternion& value)
     {
-        Quaternion result;
-        Invert(value, result);
+        Quaternion result = value;
+        result.Invert();
         return result;
     }
 

Source/Engine/Core/Math/Transform.h

@@ -155,7 +155,7 @@ public:
     /// Subtracts transformation from this transform.
     /// </summary>
     /// <param name="other">The other transformation.</param>
-    /// <returns>The different of two transformations.</returns>
+    /// <returns>The difference of two transformations.</returns>
     Transform Subtract(const Transform& other) const;
 
     /// <summary>