westwooddemuxer: Fix 1gb alloc

Fixes Ticket765
Bug Found by: Diana Elena Muscalu

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/westwood.c

@@ -320,8 +320,15 @@ static int wsvqa_read_packet(AVFormatContext *s,
     int skip_byte;
 
     while (avio_read(pb, preamble, VQA_PREAMBLE_SIZE) == VQA_PREAMBLE_SIZE) {
+        int64_t filesize= avio_size(s->pb);
         chunk_type = AV_RB32(&preamble[0]);
         chunk_size = AV_RB32(&preamble[4]);
+
+        if(chunk_size > filesize){
+            av_log(s, AV_LOG_ERROR, "Chunk with size %d truncated\n", chunk_size);
+            chunk_size= filesize;
+        }
+
         skip_byte = chunk_size & 0x01;
 
         if ((chunk_type == SND1_TAG) || (chunk_type == SND2_TAG) || (chunk_type == VQFR_TAG)) {