jabber: Fix detection of away state in choose_priority()
Thanks to this clang warning:
comparison of array 'jd->away_state->code' not equal to a null
pointer is always true [-Wtautological-pointer-compare]
Although... given how ->code is offset 0, that might have worked
sometimes if jd->away_state is null, assuming a compiler that doesn't
hate humanity. Sadly, that is not something we can safely assume.
I bet gcc saw this and thought "let's optimize your poor soul away".
