Log Message:
graphics/glw: pull latest upstream changes.

This commit incorporates a couple of bug fixes committed after the
release of libGLW 8.0.0 and before the project got eventually archived.

* Fix typo misplacing height for width.
* Fix bug with NULL variable when `glwDrawingAreaWidgetClass' is not
  found elsewhere and is assumed to be a definition (follwing the
  removal of extern declaration). See:
  https://marc.info/?l=cygwin-xfree&m=141268983004514&w=2