Add maintenance query to remove memid=0 emails

This commit introduces a fix for wrongly inserted email addresses that
have a memid=0 field because of MariaDBs strict mode that was enabled
after moving from MySQL to MariaDB.

Fixes https://bugs.cacert.org/view.php?id=1543

scripts/cron/removedead.php

@@ -39,6 +39,12 @@
 			(UNIX_TIMESTAMP(NOW()) - UNIX_TIMESTAMP(`created`)) >= 172800";
 	mysql_query($query);
 
+	// removes entries that where introduced due to missing/wrong default value
+	// in MariaDB strict mode, see https://bugs.cacert.org/view.php?id=1543
+	$query = "delete from `email` where `memid`=0 and
+			(UNIX_TIMESTAMP(NOW()) - UNIX_TIMESTAMP(`created`)) >= 172800";
+	mysql_query($query);
+
 	$query = "delete from `disputedomain` where `hash`!='' and
 			(UNIX_TIMESTAMP(NOW()) - UNIX_TIMESTAMP(`created`)) >= 21600";
 	mysql_query($query);