av_memcpy_backptr: avoid an infinite loop for back = 0

CC:libav-stable@libav.org

diff --git a/libavutil/mem.c b/libavutil/mem.c
index 3a4433d154434e346e1c3ff7975c179f30874d93..391eb7db38e8629c2cc184b3143a95246b99b1e2 100644 (file)
--- a/libavutil/mem.c
+++ b/libavutil/mem.c
@@ -252,6 +252,9 @@ static void fill32(uint8_t *dst, int len)
 void av_memcpy_backptr(uint8_t *dst, int back, int cnt)
 {
     const uint8_t *src = &dst[-back];
+    if (!back)
+        return;
+
     if (back == 1) {
         memset(dst, *src, cnt);
     } else if (back == 2) {