installer: remove duplicate mail_forwarding prior to adding unique key

install/patches/upd_0094.php

+<?php
+
+if(!defined('INSTALLER_RUN')) die('Patch update file access violation.');
+
+class upd_0094 extends installer_patch_update {
+
+	public function onBeforeSQL() {
+		global $inst;
+
+		// Remove any duplicate mail_forwardings prior to adding unique key
+		$inst->db->query("DELETE FROM mail_forwarding WHERE forwarding_id IN (SELECT forwarding_id FROM (SELECT forwarding_id, COUNT(source) AS source_count FROM mail_forwarding GROUP BY source HAVING source_count > 1) as t1)");
+	}
+
+}