nut: fix int32 overflow

Fixes CID700574
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/nut.c

@@ -155,7 +155,7 @@ void ff_nut_reset_ts(NUTContext *nut, AVRational time_base, int64_t val){
 }
 
 int64_t ff_lsb2full(StreamContext *stream, int64_t lsb){
-    int64_t mask = (1<<stream->msb_pts_shift)-1;
+    int64_t mask = (1ULL<<stream->msb_pts_shift)-1;
     int64_t delta= stream->last_pts - mask/2;
     return  ((lsb - delta)&mask) + delta;
 }