only update search list if timestamp for search message is greater than the buffer's modified time

shell/search-thread.sml

@@ -7,7 +7,8 @@ struct
     let
       val (buffer, searchString, time) = Mailbox.recv searchMailbox
       val searchList = SearchList.build (buffer, searchString)
-      val () = Mailbox.send (inputMailbox, InputMsg.WITH_SEARCH_LIST searchList)
+      val msg = InputMsg.WITH_SEARCH_LIST (searchList, time)
+      val () = Mailbox.send (inputMailbox, msg)
     in
       loop (searchMailbox, inputMailbox)
     end