Cocoa: Event polling did not initialize AppKit

Fixes #1218.

README.md

@@ -264,6 +264,7 @@ information on what to include when reporting a bug.
 - [Cocoa] Bugfix: Window title was lost when full screen or undecorated (#1082)
 - [Cocoa] Bugfix: Window was resized twice when entering full screen (#1085)
 - [Cocoa] Bugfix: Duplicate size events were not filtered (#1085)
+- [Cocoa] Bugfix: Event polling did not initialize AppKit if necessary (#1218)
 - [WGL] Added support for `WGL_EXT_colorspace` for OpenGL ES contexts
 - [WGL] Added support for `WGL_ARB_create_context_no_error`
 - [GLX] Added support for `GLX_ARB_create_context_no_error`

src/cocoa_window.m

@@ -1534,6 +1534,9 @@ void _glfwPlatformSetWindowOpacity(_GLFWwindow* window, float opacity)
 
 void _glfwPlatformPollEvents(void)
 {
+    if (!initializeAppKit())
+        return;
+
     for (;;)
     {
         NSEvent* event = [NSApp nextEventMatchingMask:NSEventMaskAny