Merged revisions 79912 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/1.4

........
r79912 | russell | 2007-08-17 16:01:43 -0500 (Fri, 17 Aug 2007) | 4 lines

Avoid a crash in the handling of DTMF based Caller ID.  It is valid for
ast_read to return NULL in the case that the channel has been hung up.
(crash reported by anonymouz666 on IRC in #asterisk-dev)

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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@79913 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_zap.c

@@ -6397,6 +6397,8 @@ static void *ss_thread(void *data)
 						return NULL;
 					} 
 					f = ast_read(chan);
+					if (!f)
+						break;
 					if (f->frametype == AST_FRAME_DTMF) {
 						dtmfbuf[i++] = f->subclass;
 						ast_debug(1, "CID got digit '%c'\n", f->subclass);