Cocoa: Fix window creation blocking after re-init

From 2fbb560eb7.

glfw/cocoa_init.m

@@ -565,6 +565,9 @@ int _glfwPlatformInit(void)
                              toTarget:_glfw.ns.helper
                            withObject:nil];
 
+    if (NSApp)
+        _glfw.ns.finishedLaunching = true;
+
     [GLFWApplication sharedApplication];
 
     _glfw.ns.delegate = [[GLFWApplicationDelegate alloc] init];