avcodec/vp3: Add missing check for av_malloc

Since the av_malloc() may fail and return NULL pointer,
it is needed that the 's->edge_emu_buffer' should be checked
whether the new allocation is success.

Fixes: d147238 ("VP3: fix decoding of videos with stride > 2048")
Reviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
(cherry picked from commit 656cb04)

libavcodec/vp3.c

@@ -2136,8 +2136,13 @@ static int vp3_decode_frame(AVCodecContext *avctx,
     if (ff_thread_get_buffer(avctx, &s->current_frame, AV_GET_BUFFER_FLAG_REF) < 0)
         goto error;
 
-    if (!s->edge_emu_buffer)
+    if (!s->edge_emu_buffer) {
         s->edge_emu_buffer = av_malloc(9 * FFABS(s->current_frame.f->linesize[0]));
+        if (!s->edge_emu_buffer) {
+            ret = AVERROR(ENOMEM);
+            goto error;
+        }
+    }
 
     if (s->keyframe) {
         if (!s->theora) {