Do not reject LIST tags in wav with size 4.

Fixes ticket #745.
(cherry picked from commit a8e93ce4cb)

libavformat/wav.c

@@ -507,7 +507,7 @@ static int wav_read_header(AVFormatContext *s,
             goto break_loop;
         case MKTAG('L', 'I', 'S', 'T'):
             list_type = avio_rl32(pb);
-            if (size <= 4) {
+            if (size < 4) {
                 av_log(s, AV_LOG_ERROR, "too short LIST");
                 return AVERROR_INVALIDDATA;
             }