st/pbo: reject vs/fs pbo ops if rowstride < width

this pbo shader works by iterating over the framebuffer size
and storing a value to an offset for each source pixel. if the
number of pixels being written out does not correspond to fragcoord
to the extent that certain source pixels are not written at all, however,
then this method should not be used in order to avoid giving broken results

cc: mesa-stable

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30689>
(cherry picked from commit c2dcecffc5)

.pick_status.json

@@ -1034,7 +1034,7 @@
         "description": "st/pbo: reject vs/fs pbo ops if rowstride < width",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null,
         "notes": null

src/mesa/state_tracker/st_pbo.c

@@ -111,6 +111,9 @@ st_pbo_addresses_pixelstore(struct st_context *st,
    if (buf_offset % addr->bytes_per_pixel)
       return false;
 
+   if (store->RowLength && store->RowLength < addr->width)
+      return false;
+
    /* Convert to texels */
    buf_offset = buf_offset / addr->bytes_per_pixel;