libobs: Fix crash when no context

If obs was shutting down in very early in initialization like when the
X11 display is missing this context parameter might still be NULL.
Return early to allow shutdown to complete without crashing.

libobs/obs-nix-x11.c

@@ -846,6 +846,8 @@ static bool obs_nix_x11_hotkeys_platform_init(struct obs_core_hotkeys *hotkeys)
 static void obs_nix_x11_hotkeys_platform_free(struct obs_core_hotkeys *hotkeys)
 {
 	obs_hotkeys_platform_t *context = hotkeys->platform_context;
+	if (!context)
+		return;
 
 	for (size_t i = 0; i < OBS_KEY_LAST_VALUE; i++)
 		da_free(context->keycodes[i].list);