mov: Fix seeking regression in fragemnted movs.

Regression introduced in 550f7c43Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mov.c

@@ -2254,6 +2254,9 @@ static int mov_read_trex(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     trex = av_realloc(c->trex_data, (c->trex_count+1)*sizeof(*c->trex_data));
     if (!trex)
         return AVERROR(ENOMEM);
+
+    c->fc->duration = AV_NOPTS_VALUE; // the duration from mvhd is not representing the whole file when fragments are used.
+
     c->trex_data = trex;
     trex = &c->trex_data[c->trex_count++];
     avio_r8(pb); /* version */