Round up subsampled frame size in av1_loop_restoration_corners_in_sb

The previous code converted a frame_w (say) of 1 to zero for a plane
where subsampling was enabled, causing a division by zero in
av1_get_rest_ntiles. This doesn't match the spec, which says
subsampling rounds up.

The patch adds the rounding, and also adds an assertion to
av1_get_rest_ntiles to help diagnose any other broken callsites.

Change-Id: Ia6c249fa935c3a16d122ba6e7b450fe99f412fde

av1/common/restoration.c

diff --git a/av1/common/restoration.c b/av1/common/restoration.c
index f97cf5b..f1411db 100644
--- a/av1/common/restoration.c
+++ b/av1/common/restoration.c
@@ -1463,8 +1463,11 @@
   const int denom = 1;
 #endif  // CONFIG_FRAME_SUPERRES
 
-  const int ss_frame_w = frame_w >> (plane > 0 && cm->subsampling_x != 0);
-  const int ss_frame_h = frame_h >> (plane > 0 && cm->subsampling_y != 0);
+  const int ss_x = plane > 0 && cm->subsampling_x != 0;
+  const int ss_y = plane > 0 && cm->subsampling_y != 0;
+
+  const int ss_frame_w = (frame_w + ss_x) >> ss_x;
+  const int ss_frame_h = (frame_h + ss_y) >> ss_y;
 
   int rtile_w, rtile_h, nvtiles;
   av1_get_rest_ntiles(ss_frame_w, ss_frame_h,

av1/common/restoration.h

diff --git a/av1/common/restoration.h b/av1/common/restoration.h
index b3f9b69..9eee959 100644
--- a/av1/common/restoration.h
+++ b/av1/common/restoration.h
@@ -194,6 +194,8 @@
   int tile_width_, tile_height_;
   tile_width_ = (tilesize < 0) ? width : AOMMIN(tilesize, width);
   tile_height_ = (tilesize < 0) ? height : AOMMIN(tilesize, height);
+  assert(tile_width_ > 0 && tile_height_ > 0);
+
   nhtiles_ = (width + (tile_width_ >> 1)) / tile_width_;
   nvtiles_ = (height + (tile_height_ >> 1)) / tile_height_;
   if (tile_width) *tile_width = tile_width_;