imap: fixed buggy names in generated URLs

For some reason the ImapUser variable gets emptied every one mailbox that gets
parsed. This produces the generated URLs to be not consistent among them,
generating, for example, "imaps://host.com/FolderA" and then
"imaps://user@host.com/FolderB". I haven't find the root cause of the problem,
but this at least fixes the issue temporarely

imap/command.c

@@ -774,7 +774,7 @@ static void cmd_parse_lsub (IMAP_DATA* idata, char* s)
   imap_quote_string(errstr, sizeof (errstr), list.name);
   url.path = errstr + 1;
   url.path[strlen(url.path) - 1] = '\0';
-  if (!mutt_strcmp (url.user, ImapUser))
+  if (mutt_strcmp (url.user, ImapUser))
     url.user = NULL;
   url_ciss_tostring (&url, buf + 11, sizeof (buf) - 10, 0);
   safe_strcat (buf, sizeof (buf), "\"");