Left top position will be set to zero.
It is a common pattern to define `BRect` value with only width and height so it allow to simplify code a bit.
Change-Id: Ie14644843324c9e5bcc55e7cfbd557a8884559d3
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8535
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>