avformat/flvdec: Do not check last size if it could not be read due to EOF

Fixes part of Ticket5648
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/flvdec.c

@@ -1141,6 +1141,7 @@ retry_duration:
 leave:
     last = avio_rb32(s->pb);
     if (last != orig_size + 11 && last != orig_size + 10 &&
+        !avio_feof(s->pb) &&
         (last != orig_size || !last) && last != flv->sum_flv_tag_size &&
         !flv->broken_sizes) {
         av_log(s, AV_LOG_ERROR, "Packet mismatch %d %d %d\n", last, orig_size + 11, flv->sum_flv_tag_size);

tests/ref/fate/flv-demux

@@ -612,3 +612,4 @@
 0,      11612,      11612,       33,     1078, 0x501d1c72, F=0x0
 0,      11645,      11645,       33,     2600, 0xdf370d24, F=0x0
 1,      11656,      11656,       46,      346, 0x8899a188
+0,      11678,      11678,       33,     1190, 0xdc1e4c99, F=0x0