[weston] Some static analysis fixes

[Rob Bradford]

Here are some patches for some issues found with a static analysis tool. These
issues are all pretty minor (the more serious issues were dealt with under my
previous patch set and also a set from John Kåre Alsaker.)

For some of these issues the added complexity / code-churn may not be
worth it - but i'll leave that decision in your hands.

Cheerio,

Rob