Fix case-changing when characters don't have an othercase character.
Fix case-changing when characters don't have an othercase character.

The character LATIN SMALL LETTER SHARP S is lower-case but has no simple
(single character) uppercase equivalent. CHAR-UPCASE was incorrectly
returning #\Null for it & similar characters.

froggey/Mezzano,froggey/Mezzano,varjagg/Mezzano,rvedam/Mezzano,varjagg/Mezzano,rvedam/Mezzano