g723_1: save/restore excitation with offset to store LPC history

The same buffer with saved data is used later in LPC reconstruction, so
it should have some head space for LPC history.

libavcodec/g723_1.c

@@ -1071,7 +1071,7 @@ static int g723_1_decode_frame(AVCodecContext *avctx, void *data,
             vector_ptr = p->excitation + PITCH_MAX;
 
             /* Save the excitation */
-            memcpy(p->audio, vector_ptr, FRAME_LEN * sizeof(*p->audio));
+            memcpy(p->audio + LPC_ORDER, vector_ptr, FRAME_LEN * sizeof(*p->audio));
 
             p->interp_index = comp_interp_index(p, p->pitch_lag[1],
                                                 &p->sid_gain, &p->cur_gain);
@@ -1086,7 +1086,7 @@ static int g723_1_decode_frame(AVCodecContext *avctx, void *data,
             /* Restore the original excitation */
             memcpy(p->excitation, p->prev_excitation,
                    PITCH_MAX * sizeof(*p->excitation));
-            memcpy(vector_ptr, p->audio, FRAME_LEN * sizeof(*vector_ptr));
+            memcpy(vector_ptr, p->audio + LPC_ORDER, FRAME_LEN * sizeof(*vector_ptr));
 
             /* Peform pitch postfiltering */
             if (p->postfilter)