fix msg search

app/controllers/Msg.scala

@@ -49,7 +49,7 @@ final class Msg(
 
   def search(q: String) = Auth { _ => me =>
     q.trim.some.filter(_.size > 1).filter(lila.user.User.couldBeUsername) match {
-      case None    => BadRequest(jsonError("Invalid search query")).fuccess
+      case None    => env.msg.json.searchResult(me)(env.msg.search.empty) map { Ok(_) }
       case Some(q) => env.msg.search(me, q) flatMap env.msg.json.searchResult(me) map { Ok(_) }
     }
   }

modules/msg/src/main/MsgSearch.scala

@@ -26,6 +26,8 @@ final class MsgSearch(
           )
     }
 
+  val empty = MsgSearch.Result(Nil, Nil, Nil)
+
   private def searchThreads(me: User, q: String): Fu[List[MsgThread]] =
     colls.thread.ext
       .find(