Windows ClientRectangle: update position in setter

Fixed the ClientRectangle setter on Windows to take the passed
rectangle's position into account.
X11 ClientRectangle: update position in setter

Fixed the ClientRectangle setter on X11 to take the passed
rectangle's position into account.
Merge pull request #1 from elisee/fix-client-rectangle-setter

Fix ClientRectangle setter on Windows (WinGL) & Linux (X11)