Fix a possible crash in sip/reqresp_parser.c that is caused by a possible null

value.

(closes issue #18821)
Reported by: cmaj
Patches: 
      patch-reqresp_parser_sip_uri_domain_cmp_c_locale-crash-1.8.3-rc2.diff.tx
      uploaded by cmaj (license 830)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@311612 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/sip/reqresp_parser.c

@@ -2009,7 +2009,11 @@ static int sip_uri_domain_cmp(const char *host1, const char *host2)
 	 */
 	if (!addr1_parsed) {
 #ifdef HAVE_XLOCALE_H
-		return strcasecmp_l(host1, host2, c_locale);
+		if(!c_locale) {
+			return strcasecmp(host1, host2);
+		} else {
+			return strcasecmp_l(host1, host2, c_locale);
+		}
 #else
 		return strcasecmp(host1, host2);
 #endif