g723_1: fix upper bound parameter from inverse maximum autocorrelation

libavcodec/g723_1.c

@@ -630,7 +630,10 @@ static int autocorr_max(G723_1_Context *p, int offset, int *ccr_max,
     int i;
 
     pitch_lag = FFMIN(PITCH_MAX - 3, pitch_lag);
-    limit     = FFMIN(FRAME_LEN + PITCH_MAX - offset - length, pitch_lag + 3);
+    if (dir > 0)
+        limit = FFMIN(FRAME_LEN + PITCH_MAX - offset - length, pitch_lag + 3);
+    else
+        limit = pitch_lag + 3;
 
     for (i = pitch_lag - 3; i <= limit; i++) {
         ccr = dot_product(buf, buf + dir * i, length, 1);