測試 libchewing-0.7.0-rc.1 的時候發現的 如果 `chewing_new` 回傳 null 的話, ibus-chewing 會進入一個無窮迴圈 Found while testing libchewing-0.7.0-rc.1. If `chewing_new` returns null then ibus-chewing will enter a infinite loop. We should check return values and handle them.