Missing call to removeObserver:

As noted in the documentation for nsdistributednotificationcenter,
(under the Discussion heading) before an observer is deallocated
a call should be made to removeObserver: in order to ensure
that all the listener is unbound from all observation pools
correctly. I can confirm that this fixes #817 for me.

https://developer.apple.com/reference/foundation/nsdistributednotificationcenter/1416236-removeobserver?language=objc

src/cocoa_init.m

@@ -359,6 +359,8 @@ void _glfwPlatformTerminate(void)
             removeObserver:_glfw.ns.listener
                       name:(__bridge NSString*)kTISNotifySelectedKeyboardInputSourceChanged
                     object:nil];
+        [[NSDistributedNotificationCenter defaultCenter]
+            removeObserver:_glfw.ns.listener];
         [_glfw.ns.listener release];
         _glfw.ns.listener = nil;
     }