apetag: Fix APE tag size check

The size variable is (correctly) unsigned, but is passed to several functions
which take signed parameters, such as avio_read, sometimes after having
numbers added to it. So ensure that size remains within the bounds that
these functions can handle.

CC: libav-stable@libav.org
Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavformat/apetag.c

@@ -57,8 +57,10 @@ static int ape_tag_read_field(AVFormatContext *s)
         av_log(s, AV_LOG_WARNING, "Invalid APE tag key '%s'.\n", key);
         return -1;
     }
-    if (size >= UINT_MAX)
-        return -1;
+    if (size > INT32_MAX - FF_INPUT_BUFFER_PADDING_SIZE) {
+        av_log(s, AV_LOG_ERROR, "APE tag size too large.\n");
+        return AVERROR_INVALIDDATA;
+    }
     if (flags & APE_TAG_FLAG_IS_BINARY) {
         uint8_t filename[1024];
         enum AVCodecID id;