Fix unknown variable message when the user has never logged in before (tested with dovecot).

functions/imap_mailbox.php

@@ -818,6 +818,7 @@ function sqimap_get_mailboxes($imap_stream,$force=false,$show_only_subscribed=tr
         sqgetGlobalVar($sub_cache_name,$lsub_cache,SQ_SESSION);
     }
 
+    $lsub_assoc_ary=array();
     if (!empty($lsub_cache)) {
         $lsub_assoc_ary=$lsub_cache;
     } else {
@@ -1303,4 +1304,4 @@ function sqimap_mailbox_is_noinferiors($oImapStream,$sImapFolder,&$oBoxes) {
     return false;
 }
 
-?>
+?>