[osx] Fix possible corruption when joystick connects early

device_add_callback could fire before the joysticks vector is
initialized if the controller is already enabled and connects instantly.

Author: connorjclark

src/macosx/hidjoy.m

@@ -811,6 +811,8 @@ static bool init_joystick(void)
    CFRelease(criteria1);
    CFRelease(criteria);
 
+   _al_vector_init(&joysticks, sizeof(ALLEGRO_JOYSTICK_OSX *));
+
    /* Register for plug/unplug notifications */
    IOHIDManagerRegisterDeviceMatchingCallback(
       hidManagerRef,
@@ -836,8 +838,6 @@ static bool init_joystick(void)
       kCFRunLoopDefaultMode
    );
 
-   _al_vector_init(&joysticks, sizeof(ALLEGRO_JOYSTICK_OSX *));
-
    al_lock_mutex(add_mutex);
 
    IOReturn ret = IOHIDManagerOpen(