stop listening on old recipient changes

Closes #4251
// FREEBIE

src/org/thoughtcrime/securesms/ConversationActivity.java

@@ -927,6 +927,8 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
   }
 
   private void initializeResources() {
+    if (recipients != null) recipients.removeListener(this);
+    
     recipients       = RecipientFactory.getRecipientsForIds(this, getIntent().getLongArrayExtra(RECIPIENTS_EXTRA), true);
     threadId         = getIntent().getLongExtra(THREAD_ID_EXTRA, -1);
     distributionType = getIntent().getIntExtra(DISTRIBUTION_TYPE_EXTRA, ThreadDatabase.DistributionTypes.DEFAULT);