ignore untagged/wildcard/unknown MLs in delete with via-branch

fixes #840

Change-Id: Ifddf6c4c5ae58556dc9a746f657c7aebc4beee67
(cherry picked from commit 7b60ca8e35)

daemon/call.c

@@ -2750,7 +2750,7 @@ int call_delete_branch(const str *callid, const str *branch,
 	if ((!totag || !totag->len) && branch && branch->len) {
 		// try a via-branch match
 		ml = g_hash_table_lookup(c->viabranches, branch);
-		if (ml)
+		if (ml && ml->tag.len) // ignore wildcard/unknown monologues
 			goto do_delete;
 	}