res_fax_spandsp: Properly handle cleanup before starting FAXes.

If faxing fails at a very early stage, then it is possible for
us to pass a NULL t30 state pointer to spandsp, which spandsp
is none too pleased with.

This patch ensures that we pass the correct pointer to spandsp
in the situation where we have not yet set our local t30 state
pointer.

ASTERISK-24301 #close
Reported by Matt Jordan
Patches:
	ASTERISK-24301-fax.diff Uploaded by Mark Michelson (License #5049)




git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@423360 65c4cc65-6c06-0410-ace0-fbb531ad65f3