fixes segfault in iLBC

For reasons not yet known, it appears possible for an ast_frame
to have a datalen greater than zero while the actual data is NULL
during Packet Loss Concealment.  Most codecs don't support PLC so
this doesn't affect them.  This patch catches the malformed frame
and prevents the crash from occuring.  Additional efforts to determine
why it is possible for a frame to look like this are still being
investigated.

(issue #16979)



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@228418 65c4cc65-6c06-0410-ace0-fbb531ad65f3

codecs/codec_ilbc.c

@@ -127,6 +127,11 @@ static int ilbctolin_framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
 	int16_t *dst = (int16_t *)pvt->outbuf;
 	float tmpf[ILBC_SAMPLES];
 
+	if (!f->data && f->datalen) {
+		ast_log(LOG_DEBUG, "issue 16070, ILIB ERROR. data = NULL datalen = %d src = %s\n", f->datalen, f->src ? f->src : "no src set");
+		f->datalen = 0;
+	}
+
 	if (f->datalen == 0) { /* native PLC, set fake f->datalen and clear plc_mode */
 		f->datalen = ILBC_FRAME_LEN;
 		f->samples = ILBC_SAMPLES;