FS-11176: [core] do not use previous codec if its not ready

src/switch_core_codec.c

@@ -235,7 +235,7 @@ SWITCH_DECLARE(switch_status_t) switch_core_session_set_read_codec(switch_core_s
 			goto end;
 		}
 
-		if (session->read_codec->next) {
+		if (session->read_codec->next && switch_core_codec_ready(session->read_codec->next)) {
 			switch_codec_t *old = session->read_codec;
 			session->read_codec = session->read_codec->next;
 			if (session->read_codec->implementation) {