Intermittent crash in nsNativeThemeCocoa::DrawWidgetBackground

[classilla]

This may be part of the null CGContext crashes some users have been seeing. I can reproduce it occasionally on Hacker News, though not anywhere else. Screenshot of crashdump:

[classilla]

This makes sense, since it's focusing a text control. Maybe we just don't draw anything if there's no saved context.

[classilla]

Unable to reproduce any more.