Fixed wrong warning on memory leak.

Set the auth_hdr buffer to NULL after moving the buffer into the lump.
Reported by Colin Martin on mailing list

Author: bogdan-iancu

modules/uac/auth.c

@@ -268,6 +268,9 @@ int uac_auth( struct sip_msg *msg)
 		new_hdr->s = NULL; new_hdr->len = 0;
 		goto error;
 	}
+	/* the Authorization hdr was already pushed into the message as a lump
+	 * along with the buffer, so detach the buffer from new_hdr var */
+	new_hdr->s = NULL; new_hdr->len = 0;
 
 	if ( (new_cseq = apply_cseq_op(msg,1)) < 0) {
 		LM_WARN("Failure to increment the CSEQ header - continue \n");