bridge_softmix: Ignore non-voice frames from translator

Some codecs - codec_speex specifically - take voice frames and return
other types of frames, like CNG. If we subsequently treat those as
voice frames, we'll run into trouble when destroying the frame because
of the requirement that each voice frame have an associated format.

ASTERISK-26880 #close
Reported by: Kirsty Tyerman

Change-Id: I43f8450c48fb276ad8b99db8512be82949c1ca7c

bridges/bridge_softmix.c

@@ -222,7 +222,8 @@ static void softmix_process_write_audio(struct softmix_translate_helper *trans_h
 		if (entry->trans_pvt && !entry->out_frame) {
 			entry->out_frame = ast_translate(entry->trans_pvt, &sc->write_frame, 0);
 		}
-		if (entry->out_frame && (entry->out_frame->datalen < MAX_DATALEN)) {
+		if (entry->out_frame && entry->out_frame->frametype == AST_FRAME_VOICE
+				&& entry->out_frame->datalen < MAX_DATALEN) {
 			ao2_replace(sc->write_frame.subclass.format, entry->out_frame->subclass.format);
 			memcpy(sc->final_buf, entry->out_frame->data.ptr, entry->out_frame->datalen);
 			sc->write_frame.datalen = entry->out_frame->datalen;