dshow: avoid integer overflow when using curbufsize

Signed-off-by: rogerdpack <rogerpack2005@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/dshow.c

@@ -46,7 +46,7 @@ struct dshow_ctx {
     HANDLE event;
     AVPacketList *pktl;
 
-    unsigned int curbufsize;
+    int64_t curbufsize;
     unsigned int video_frame_num;
 
     IMediaControl *control;