avformat/vqf: check avio_read()s return value more completely

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f180a523a71_5052_esvorbei_extd.vqf
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/vqf.c

@@ -249,7 +249,7 @@ static int vqf_read_packet(AVFormatContext *s, AVPacket *pkt)
     pkt->data[1] = c->last_frame_bits;
     ret = avio_read(s->pb, pkt->data+2, size);
 
-    if (ret<=0) {
+    if (ret != size) {
         av_free_packet(pkt);
         return AVERROR(EIO);
     }