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)
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git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@423380 f38db490-d61c-443f-a65b-d21fe96a405b
Add API call to determine if format capability structure is "empty".

Empty here means that there are no formats in the format_cap structure
or the only format in it is the "none" format.

I've added calls to check the emptiness of a format_cap in a few places
in order to short-circuit operations that would otherwise be pointless
as well as to prevent some assertions from being triggered in cases
where channels with no formats are used.
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astobj2.c/refcounter.py: Fix to deal with invalid object refs.

* Make astob2 REF_DEBUG output an invalid object line when an invalid ao2
object ref/unref is attempted.  This is similar to the
constructor/destructor lines.

* Fixed refcounter.py to handle skewed objects that have
constructor/destructor states.

* Made refcounter.py highlight the invalid ao2 object refs by putting them
in their own section of the processed output file.

* Made refcounter.py highlight unreffing an object by more than one that
results in a negative ref count and the object being destroyed.  The
abnormally destroyed object is reported in the invalid and finalized
object sections of the output.

Review: https://reviewboard.asterisk.org/r/3971/
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