[OSX] catch exceptions when window closed and tries to lockFocusIfCanDraw.

native/Avalonia.Native/src/OSX/gl.mm

@@ -233,8 +233,17 @@ public:
         auto f = GetFeature();
         if(f == NULL)
             return E_FAIL;
-        if(![_view lockFocusIfCanDraw])
+        
+        @try
+        {
+            if(![_view lockFocusIfCanDraw])
+                return E_ABORT;
+        }
+        @catch(NSException* exception)
+        {
             return E_ABORT;
+        }
+        
         
         auto gl = _context;
         CGLLockContext([_context CGLContextObj]);

native/Avalonia.Native/src/OSX/window.mm

@@ -291,7 +291,14 @@ public:
     {
         @autoreleasepool
         {
-            return [View lockFocusIfCanDraw] == YES;
+            @try
+            {
+                return [View lockFocusIfCanDraw] == YES;
+            }
+            @catch (NSException*)
+            {
+                return NO;
+            }
         }
     }