w64dec: fix end position of summarylist guid

Noticed-by: James Almer
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavformat/wavdec.c

@@ -674,7 +674,7 @@ static int w64_read_header(AVFormatContext *s)
             uint32_t count, chunk_size, i;
 
             start = avio_tell(pb);
-            end = start + size;
+            end = start + FFALIGN(size, INT64_C(8)) - 24;
             count = avio_rl32(pb);
 
             for (i = 0; i < count; i++) {