After all the LogicalFontInstance refactoring, its FontSelectData
is now immutable, so the HFONT will never need to be changed.
Therefore we can skip the HFONT lookup in WinSalGraphics::SetFont,
if the WinFontInstance already has it set.

All the HFONT handling (basically WinSalGraphics::ImplDoSetFont)
should be moved to the WinFontInstance to further clean this up.

Change-Id: I1c9a9e3414677d77f0f007d7ace653bb53b8474d
Reviewed-on: https://gerrit.libreoffice.org/59988
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>