misc.search: catch empty queries

src/modules/misc.js

@@ -554,6 +554,7 @@ search.addAlias("google");
 search.addAlias("ddg");
 search.callback = async function (msg, line) {
   if (!librex) return "LibreX instance not defined.";
+  if (!line || line == "") return "Search query required.";
 
   const query = encodeURIComponent(line);