windows opengl: Printer still needs WinSalGraphicsImpl.

Change-Id: I298783d5f1c7e825f52eb3d61f45c0c3d3019f04
opengl: Check for error at the end of every method that deals with OpenGL.

Otherwise we will get the report of an error much much later, most probably in
a totally unrelated part.

Change-Id: I33d3c6d01126f5766beb179eeaeb3276a9078226