extra protection against unruly practice

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@8313 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/switch_core_io.c

@@ -501,6 +501,10 @@ SWITCH_DECLARE(switch_status_t) switch_core_session_write_frame(switch_core_sess
 		return SWITCH_STATUS_FALSE;
 	}
 
+	if (!(session->write_codec && session->write_codec->implementation)) {
+		return SWITCH_STATUS_FALSE;
+	}
+
 	if (switch_channel_test_flag(session->channel, CF_HOLD)) {
 		return SWITCH_STATUS_SUCCESS;
 	}