fixed incorrect name for close-pressed.png for windows in black theme (#12563)

The scss file and the light and normal style suggest that the name should be
"-pressed". This is what this patch fixes. I have considered renaming all
"-pressed" to "-active", to be consistent with e.g. "maximize-active.png"
but decided against due to compatibility concerns.

Change-Id: I42f37b3311715fab04e5fe05fdf4bc3026e52ed1