avformat/oggparseogm: Fix undefined shift in ogm_packet()

Fixes: shift exponent 48 is too large for 32-bit type 'int'
Fixes: Chromium bug 786793
Reported-by: Matt Wolenetz <wolenetz@google.com>
Reviewed-by: Matt Wolenetz <wolenetz@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/oggparseogm.c

@@ -180,7 +180,7 @@ ogm_packet(AVFormatContext *s, int idx)
     os->psize -= lb + 1;
 
     while (lb--)
-        os->pduration += p[lb+1] << (lb*8);
+        os->pduration += (uint64_t)p[lb+1] << (lb*8);
 
     return 0;
 }