Add default: break; to switches on SDL_Event::type

This is just a nice-to-have, as `SDL_Event::type` in an `Uint32`, so there are no
compiler errors about not handling all `SDL_EventType` enum values.

test/testhotplug.c

@@ -155,6 +155,8 @@ int main(int argc, char *argv[])
             case SDL_EVENT_JOYSTICK_BUTTON_UP:
                 SDL_Log("Button Release: %d\n", event.jbutton.button);
                 break;
+            default:
+                break;
             }
         }
     }