format.c: correct possible null pointer dereference

In ast_format_sdp_parse and ast_format_sdp_generate
the check checks for a valid interface and function
were potentially confusing, and hid an error in the
test of the presence of the function that is called
later.  This patch clears up and corrects the test.

Review: https://reviewboard.asterisk.org/r/3208/
(closes issue ASTERISK-23098)
Reported by: marcelloceschia
Patches:
     main_format.patch uploaded by marcelloceschia (license 6036)
	 ASTERISK-23098.patch uploaded by coreyfarrell (license 5909)
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Merged revisions 408137 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 408138 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@408139 f38db490-d61c-443f-a65b-d21fe96a405b
ARI: correct upper/lower case URI discrepancies

URI's are supposed to be case sensitive and all
lower case.  In practice some portions of URI's
in ARI are case insensitive and others are not,
such as TECH, which in one instance would match
a lower case name and in another would not.  In
this patch, the ast_endpoint_lastest_snapshot()
function is modified to change the TECH portion
to full upper case before lookup. This resolves
the discrepancy noted by the reporter.  However
I chose to avoid forcing the /ari prefix of the
URI's to be lower case for now.  Except for the
two cases here, all URI's should be lower case,
unless they are part of a resource name or id.

Review: https://reviewboard.asterisk.org/r/3211/
Reported by: Zane Conkle
(closes issue ASTERISK-23125)
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Merged revisions 408140 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@408141 f38db490-d61c-443f-a65b-d21fe96a405b