st/nine: Don't call u_box_union_* when dirty region is empty

When dirty region is empty, u_box_union_* incorrectly expands
the new region.

This fixes broken font rendering issue in WOLF RPG Editor v2.10 games.

Signed-off-by: Masanori Kakura <kakurasan@gmail.com>
Reviewed-by: Axel Davy <axel.davy@ens.fr>
diff --git a/src/gallium/state_trackers/nine/cubetexture9.c b/src/gallium/state_trackers/nine/cubetexture9.c
index 977a345..65251ad 100644
--- a/src/gallium/state_trackers/nine/cubetexture9.c
+++ b/src/gallium/state_trackers/nine/cubetexture9.c
@@ -285,10 +285,14 @@
                         This->base.base.info.height0,
                         &This->dirty_rect[FaceType]);
     } else {
-        struct pipe_box box;
-        rect_to_pipe_box_clamp(&box, pDirtyRect);
-        u_box_union_2d(&This->dirty_rect[FaceType], &This->dirty_rect[FaceType],
-                       &box);
+        if (This->dirty_rect[FaceType].width == 0) {
+            rect_to_pipe_box_clamp(&This->dirty_rect[FaceType], pDirtyRect);
+        } else {
+            struct pipe_box box;
+            rect_to_pipe_box_clamp(&box, pDirtyRect);
+            u_box_union_2d(&This->dirty_rect[FaceType], &This->dirty_rect[FaceType],
+                           &box);
+        }
         (void) u_box_clip_2d(&This->dirty_rect[FaceType],
                              &This->dirty_rect[FaceType],
                              This->base.base.info.width0,
diff --git a/src/gallium/state_trackers/nine/texture9.c b/src/gallium/state_trackers/nine/texture9.c
index bf054cc..78ca4ad 100644
--- a/src/gallium/state_trackers/nine/texture9.c
+++ b/src/gallium/state_trackers/nine/texture9.c
@@ -330,9 +330,13 @@
         u_box_origin_2d(This->base.base.info.width0,
                         This->base.base.info.height0, &This->dirty_rect);
     } else {
-        struct pipe_box box;
-        rect_to_pipe_box_clamp(&box, pDirtyRect);
-        u_box_union_2d(&This->dirty_rect, &This->dirty_rect, &box);
+        if (This->dirty_rect.width == 0) {
+            rect_to_pipe_box_clamp(&This->dirty_rect, pDirtyRect);
+        } else {
+            struct pipe_box box;
+            rect_to_pipe_box_clamp(&box, pDirtyRect);
+            u_box_union_2d(&This->dirty_rect, &This->dirty_rect, &box);
+        }
         (void) u_box_clip_2d(&This->dirty_rect, &This->dirty_rect,
                              This->base.base.info.width0,
                              This->base.base.info.height0);
diff --git a/src/gallium/state_trackers/nine/volumetexture9.c b/src/gallium/state_trackers/nine/volumetexture9.c
index 5c83fdb..c836dd2 100644
--- a/src/gallium/state_trackers/nine/volumetexture9.c
+++ b/src/gallium/state_trackers/nine/volumetexture9.c
@@ -222,9 +222,13 @@
         This->dirty_box.height = This->base.base.info.height0;
         This->dirty_box.depth = This->base.base.info.depth0;
     } else {
-        struct pipe_box box;
-        d3dbox_to_pipe_box(&box, pDirtyBox);
-        u_box_union_3d(&This->dirty_box, &This->dirty_box, &box);
+        if (This->dirty_box.width == 0) {
+            d3dbox_to_pipe_box(&This->dirty_box, pDirtyBox);
+        } else {
+            struct pipe_box box;
+            d3dbox_to_pipe_box(&box, pDirtyBox);
+            u_box_union_3d(&This->dirty_box, &This->dirty_box, &box);
+        }
         This->dirty_box.x = MAX2(This->dirty_box.x, 0);
         This->dirty_box.y = MAX2(This->dirty_box.y, 0);
         This->dirty_box.z = MAX2(This->dirty_box.z, 0);