When \XeTeXupwards mode is active (non-zero) line spacing calculations are inverted, that is the lineskip is calculated as \baselineskip - height(line-1) - depth(line), instead of the normal \baselineskip - depth(line-1) - height(line). This works fine. But the lineskip calculation at the top of a page or vsplit needs also to be inverted. This PR fixes that.
When \XeTeXupwards mode is active (non-zero) line spacing calculations are inverted, that is the lineskip is calculated as \baselineskip - height(line-1) - depth(line), instead of the normal \baselineskip - depth(line-1) - height(line). This works fine. But the lineskip calculation at the top of a page or vsplit needs also to be inverted. This PR fixes that.