lavu/buffer: forward av_buffer_realloc() error code.

Fix CID 1457235.

libavutil/buffer.c

@@ -170,6 +170,7 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
 {
     AVBufferRef *buf = *pbuf;
     uint8_t *tmp;
+    int ret;
 
     if (!buf) {
         /* allocate a new buffer with av_realloc(), so it will be reallocatable
@@ -196,9 +197,9 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
         /* cannot realloc, allocate a new reallocable buffer and copy data */
         AVBufferRef *new = NULL;
 
-        av_buffer_realloc(&new, size);
+        ret = av_buffer_realloc(&new, size);
-        if (!new)
+        if (ret < 0)
-            return AVERROR(ENOMEM);
+            return ret;
 
         memcpy(new->data, buf->data, FFMIN(size, buf->size));