Fix issue on conversation update

lib/helpers/conversations_helper.dart

@@ -58,7 +58,14 @@ class ConversationsHelper {
 
     final response = await request.exec();
 
-    return response.code == 200;
+    if(response.code != 200)
+      return false;
+
+    //Delete old conversation entry from the database
+    await _conversationsDatabaseHelper.delete(settings.id);
+
+    // Success
+    return true;
   }
 
   /// Delete a conversation specified by its [id]