avfilter/vf_subtitles: pass storage size to libass

Due to a quirk of the ASS format some tags depend on the exact storage
resolution of the video, so tell libass via ass_set_storage_size.
Reviewed-by: Soft Works <softworkz@hotmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

libavfilter/vf_subtitles.c

@@ -147,9 +147,13 @@ static int config_input(AVFilterLink *inlink)
     ff_draw_init(&ass->draw, inlink->format, ass->alpha ? FF_DRAW_PROCESS_ALPHA : 0);
 
     ass_set_frame_size  (ass->renderer, inlink->w, inlink->h);
-    if (ass->original_w && ass->original_h)
+    if (ass->original_w && ass->original_h) {
         ass_set_pixel_aspect(ass->renderer, (double)inlink->w / inlink->h /
                              ((double)ass->original_w / ass->original_h));
+        ass_set_storage_size(ass->renderer, ass->original_w, ass->original_h);
+    } else
+        ass_set_storage_size(ass->renderer, inlink->w, inlink->h);
+
     if (ass->shaping != -1)
         ass_set_shaper(ass->renderer, ass->shaping);