avformat/wc3movie: fix memleak when read content size not equvipe input size

Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

libavformat/wc3movie.c

@@ -130,8 +130,10 @@ static int wc3_read_header(AVFormatContext *s)
             buffer = av_malloc(size+1);
             if (!buffer)
                 return AVERROR(ENOMEM);
-            if ((ret = avio_read(pb, buffer, size)) != size)
+            if ((ret = avio_read(pb, buffer, size)) != size) {
+                av_freep(&buffer);
                 return AVERROR(EIO);
+            }
             buffer[size] = 0;
             av_dict_set(&s->metadata, "title", buffer,
                                    AV_DICT_DONT_STRDUP_VAL);