GSM codec factory does not shutdown properly causing it to fail on next pjsua_init (thanks Binu K S)

[bennylp]

The GSM codec factory refuses to shutdown itself when there are outstanding codecs in the cache, but this would always be the case if the GSM codec has ever been used! This would cause the factory to fail to unregister itself from the codec manager, and it will cause next call to get "Invalid RTP PT" error.

See this thread for reference:
​http://www.pjsip.org/pipermail/pjsip/2007-March/002523.html

Thanks Binu KS for reporting and fixing this.