dump: Trim spaces only in color mode 0 or -1
The old code failed to write pending spaces before changing the
background color. That seems hard to fix without duplicating code,
and ELinks pads dumped lines to the requested width in these color
modes anyway, so this commit just makes ELinks write all spaces
immediately when colors are being used.
Try the following command before and after this commit:
elinks --no-home --eval "set document.colors.use_document_colors = 2" \
--dump-color-mode 1 --dump test/color.html