Small performance improvement

app/src/main/kotlin/com/simplemobiletools/smsmessenger/adapters/ConversationsAdapter.kt

@@ -192,13 +192,15 @@ class ConversationsAdapter(
             return
         }
         val conversationsMarkedAsUnread = conversations.filter { selectedKeys.contains(it.hashCode()) } as ArrayList<Conversation>
-        conversationsMarkedAsUnread.forEach {
+        ensureBackgroundThread {
+            conversationsMarkedAsUnread.filter { el -> el.read }.forEach {
                 activity.markThreadMessagesUnread(it.threadId)
             }
             activity.runOnUiThread {
                 refreshMessages()
                 finishActMode()
             }
+        }
 
     }