This used to work only for 0- and 1-pixel wide handles. However,
and paradoxically, 2- and 3-pixel wide handles would end up with
narrower grab areas. We now ensure a 4 or 5 minimum grab area,
depending on the handle width parity.
The patch also clears the margins and mask if the handle size is
increased at some point.
Change-Id: I8a16e39fb34b5452d9021dbde8c22bec79df0243
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
2f797f8a91