cocoa-cb: fix race condition on quit

it was possible for mouse events to be triggered when the core was
already being shut down. to prevent this properly close and remove the
window and additional remove the reference to MPVHelper object.

video/out/cocoa_cb_common.swift

@@ -574,6 +574,7 @@ class CocoaCB: NSObject {
         }
         if isShuttingDown { return }
 
+        uninit()
         setCursorVisiblility(true)
         stopDisplaylink()
         uninitLightSensor()