MacOS: When initializing an openGL view with a parent window, call finishInit

src/SFML/Window/OSX/SFWindowController.mm

@@ -123,6 +123,8 @@
 
         // Set the view to the window as its content view.
         [m_window setContentView:m_oglView];
+        
+        [m_oglView finishInit];
     }
 
     return self;