Fix group deletion

app/src/main/java/org/thoughtcrime/securesms/loki/api/PublicChatManager.kt

@@ -150,9 +150,10 @@ class PublicChatManager(private val context: Context) {
     val groupId = "$server.$room"
     val threadId = GroupManager.getOpenGroupThreadID(groupId, context)
     val groupAddress = threadDB.getRecipientForThreadId(threadId)!!.address.serialize()
-    GroupManager.deleteGroup(groupAddress, context)
-
-    Util.runOnMain { startPollersIfNeeded() }
+    ThreadUtils.queue {
+      GroupManager.deleteGroup(groupAddress, context) // Must be invoked on a background thread
+      Util.runOnMain { startPollersIfNeeded() }
+    }
   }
 
   private fun refreshChatsAndPollers() {