modules/m_oper.c: give a better error message for failure to find o:line

The snotice sent to other opers can be misleading. For example, it will say
host mismatch even if the host is correct but the username is wrong, or if
the oper name given does not exist in the configuration.

modules/m_oper.c

@@ -107,8 +107,8 @@ m_oper(struct MsgBuf *msgbuf_p, struct Client *client_p, struct Client *source_p
 		if(ConfigFileEntry.failed_oper_notice)
 		{
 			sendto_realops_snomask(SNO_GENERAL, L_NETWIDE,
-					     "Failed OPER attempt - host mismatch by %s (%s@%s)",
-					     source_p->name, source_p->username, source_p->host);
+					     "Failed OPER attempt - user@host mismatch or no operator block for %s by %s (%s@%s)",
+					     name, source_p->name, source_p->username, source_p->host);
 		}
 
 		return;