Option to disable writing mda to database (#38)

Author: hoewer

README.md

@@ -59,7 +59,7 @@ In case you need to edit default-set settings, you may copy `config.inc.php.dist
 * `$config['fetchmail_db_dsn']` allows you to use a fetchmail database outside the Roundcube database, e.g. from an existing Postfix Admin installation. see [Roundcube configuration options](https://github.com/roundcube/roundcubemail/wiki/Configuration#database-connection) for correct syntax. If set to `null`, Roundcube Database is used. Default is `null`.
 * `$config['fetchmail_folder']` whether to allow users to specify IMAP folder they wish to download mail from. Default is `false`.
 * `$config['fetchmail_limit']` limits the number of external mailboxes per user allowed. Default is `10`.
-* `$config['fetchmail_mda']` allows you to specify mda field for fetchmail. This could be useful in case you want to deliver downloaded mail via MDA or LDA directly, rather than forwarding via SMTP or LMTP. For more information please refer to [fetchmail manual](http://www.fetchmail.info/fetchmail-man.html) and [fetchmail.pl](https://github.com/postfixadmin/postfixadmin/blob/master/ADDITIONS/fetchmail.pl) script. Default is `''`, i.e. not used.
+* `$config['fetchmail_mda']` allows you to specify mda field for fetchmail. This could be useful in case you want to deliver downloaded mail via MDA or LDA directly, rather than forwarding via SMTP or LMTP. For more information please refer to [fetchmail manual](http://www.fetchmail.info/fetchmail-man.html) and [fetchmail.pl](https://github.com/postfixadmin/postfixadmin/blob/master/ADDITIONS/fetchmail.pl) script. Default is `''`, i.e. mda is skipped. Possibly existing values are left untouched.
 
 ## License
 This software distributed under the terms of the GNU General Public License as published by the Free Software Foundation

fetchmail.php

@@ -175,7 +175,12 @@ public function save()
         }
         else
         {
+        	if($mda != '')
+            {
             $sql = "UPDATE fetchmail SET mailbox = '$mailbox', domain = '$mailbox_domain', active = '$enabled', keep = '$keep', protocol = '$protocol', src_server = '$server', src_user = '$user', src_password = '$pass', src_folder = '$folder', poll_time = '$pollinterval', fetchall = '$fetchall', usessl = '$usessl', src_auth = 'password', mda = '$mda' WHERE id = '$id'";
+            } else {
+            $sql = "UPDATE fetchmail SET mailbox = '$mailbox', domain = '$mailbox_domain', active = '$enabled', keep = '$keep', protocol = '$protocol', src_server = '$server', src_user = '$user', src_password = '$pass', src_folder = '$folder', poll_time = '$pollinterval', fetchall = '$fetchall', usessl = '$usessl', src_auth = 'password' WHERE id = '$id'";
+            }
             $update = $this->db->query($sql);
             if ($err_str = $this->db->is_error())
 			{