AE: Fix segfault on resume

Famous CEC Adapter plays a "tadamm" sound directly after resume. Therefore ProcessSuspend leaves out of the front door before a reOpen could have been triggered. As the ::Resume only flags m_reOpen = true, m_sink could still be NULL.

This checks takes care of this. 
Backtrace of the error is here: http://pastebin.ubuntu.com/5649014/

Thx @olympia for the time for tracking it down.