(layout_glyphs): Don't combine a zero width glyph with the previous one if the zero width glyph has left or right padding.
(layout_glyphs): Don't combine a zero width glyph with
the previous one if the zero width glyph has left or right
padding.

xmirror/m17n-lib,xmirror/m17n-lib,xmirror/m17n-lib,xmirror/m17n-lib