Make chan_zap initialize the pri threads to AST_PTHREADT_NULL and check when...

Make chan_zap initialize the pri threads to AST_PTHREADT_NULL and check when calling unload in case load_module fails complete


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3177 65c4cc65-6c06-0410-ace0-fbb531ad65f3