mov: detect EOF in mov_read_dref()

This fixes a (near) infinite loop and Ticket783
Bug found by: cosminamironesei
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mov.c

@@ -431,6 +431,8 @@ static int mov_read_dref(MOVContext *c, AVIOContext *pb, MOVAtom atom)
             avio_skip(pb, 16);
 
             for (type = 0; type != -1 && avio_tell(pb) < next; ) {
+                if(url_feof(pb))
+                    return AVERROR(EOF);
                 type = avio_rb16(pb);
                 len = avio_rb16(pb);
                 av_log(c->fc, AV_LOG_DEBUG, "type %d, len %d\n", type, len);