Free successfully translated frame in fax_gateway_framehook

A frame that is translated via ast_translate is also duplicated via ast_frdup.
This will allocate a new frame on the heap, which needs to be free'd
at the appropriate time.  This issue reporter used valgrind to find that this
occurred in res_fax's fax_gateway_framehook; a quick search through the code
showed that only place this was currently not handling the translatted frame
properly.

(closes issue ASTERISK-19133)
Reported by: Sylvain Rochet
........

Merged revisions 349608 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@349609 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_fax.c

@@ -3086,6 +3086,7 @@ static struct ast_frame *fax_gateway_framehook(struct ast_channel *chan, struct
 		 * write would fail, or even if a failure would be fatal so for
 		 * now we'll just ignore the return value. */
 		gateway->s->tech->write(gateway->s, f);
+		ast_frfree(f);
 		f = &ast_null_frame;
 		ao2_ref(details, -1);
 		return f;