rawvid: fix rounding division when calculating pitch

formats like NV12 where num and den are 2 had the wrong pitch

size is divided then multiplied, consistently with `rawvideo` decoder

(cherry-picked from commit 128f7ff6)

modules/demux/rawvid.c

@@ -356,10 +356,10 @@ valid:
     p_sys->frame_size = 0;
     for (unsigned i=0; i<dsc->plane_count; i++)
     {
-        unsigned pitch = (i_width + (dsc->p[i].w.den - 1))
-                         * dsc->p[i].w.num / dsc->p[i].w.den * dsc->pixel_size;
-        unsigned lines = (i_height + (dsc->p[i].h.den - 1))
-                         * dsc->p[i].h.num / dsc->p[i].h.den;
+        unsigned pitch = ((i_width + (dsc->p[i].w.den - 1)) / dsc->p[i].w.den)
+                          * dsc->p[i].w.num * dsc->pixel_size;
+        unsigned lines = ((i_height + (dsc->p[i].h.den - 1)) / dsc->p[i].h.den)
+                         * dsc->p[i].h.num;
         p_sys->frame_size += pitch * lines;
     }
     p_sys->p_es_video = es_out_Add( p_demux->out, &p_sys->fmt_video );