ffplay: cast vp->height to int64 in buffer size check

Fixes Coverity CID 1026769 and 1026756.
Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -1518,7 +1518,7 @@ static void alloc_picture(VideoState *is)
                                    SDL_YV12_OVERLAY,
                                    screen);
     bufferdiff = vp->bmp ? FFMAX(vp->bmp->pixels[0], vp->bmp->pixels[1]) - FFMIN(vp->bmp->pixels[0], vp->bmp->pixels[1]) : 0;
-    if (!vp->bmp || vp->bmp->pitches[0] < vp->width || bufferdiff < vp->height * vp->bmp->pitches[0]) {
+    if (!vp->bmp || vp->bmp->pitches[0] < vp->width || bufferdiff < (int64_t)vp->height * vp->bmp->pitches[0]) {
         /* SDL allocates a buffer smaller than requested if the video
          * overlay hardware is unable to support the requested size. */
         av_log(NULL, AV_LOG_FATAL,