Update Writer.php

[alexandrutabolcea]

Consider replacing empty with !isset || strlen == 0

there is a bug when translation value is "0"

if (empty($translation[$locale])) { continue; }

            if (!isset($translation[$locale]) || strlen($translation[$locale]) == 0) {
                continue;
            }

[nbourguig]

I just went a head and replace empty() by isset() only. I had some cases where I need to keep a translation empty.