fontconfig: always fall back to Arial for VSFilter compatibility
Do not substitute NBSP (\h) with a normal space

\h is often used in typesetting purely for horizontal padding.
This relies on its metrics being known. VSFilter uses the NBSP glyph
directly and substitutes Arial if it does not exist in the given
font. The previous commit dealt with the Arial substitution,
so what remains now is only to use NBSP directly.

This reverts commit 33a3ab2c8777241b73ad85024158e19fb1f9c699.
This fixes libass#42.