NULL passed to strcmp in Wayland_ShowMessageBox

src/video/wayland/SDL_waylandmessagebox.c

@@ -150,11 +150,13 @@ Wayland_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
 
     /* Check which button got pressed */
     for (i = 0; i < messageboxdata->numbuttons; i += 1) {
+        if (messageboxdata->buttons[i].text != NULL) {
             if (SDL_strcmp(output, messageboxdata->buttons[i].text) == 0) {
                 *buttonid = i;
                 break;
             }
         }
+    }
 
 end:
     SDL_free(command);