G722: Fix buffer overflow (BelledonneCommunications#20)

src/audiofilters/msg722.c

@@ -267,7 +267,7 @@ static void dec_process(MSFilter *f) {
 			/* introduce delay (TRANSITION_DELAY ms) */
 			generic_plc_update_continuity_buffer(s->plc_context, om->b_wptr, declen*sizeof(int16_t));
 
-			if (s->plc_context->plc_samples_used!=0) {
+			if (s->plc_context->plc_samples_used!=0 && declen >= 2*16*TRANSITION_DELAY) {
 				/* we were doing PLC, now resuming with normal audio, continuity buffer is twice the transition delay lengths,
 				 * the second half is untouched by the update function and contains transition data generated by PLC */
 				generic_plc_transition_mix(((int16_t *)(om->b_wptr))+16*TRANSITION_DELAY, ((int16_t *)(s->plc_context->continuity_buffer))+16*TRANSITION_DELAY, 16*TRANSITION_DELAY);