devel/rlvm: fix font handling

Even CLANNAD (Steam HD edition) didn't work[1], so...

• Force at least one supported font to be installed
• Chase paths for MONA after rename in r397892
• Don't look under PREFIX, other packages are under LOCALBASE

[1] rlvm doesn't use fontconfig, so it happily crashed without leaving

any error on terminal to assist troubleshooting if one of the listed
fonts couldn't be found.