Dawn: fix mipmap width and height computation during upload.

Don't go below 1 in width or height when downsizing for uploads.
This can happen with rectangular textures, where one dimension hits
the lower bound.

Change-Id: Ica28e6274cf1df658145233ab6694f2c64c55201
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/252316
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>
1 file changed