bug#34492: rx: ASCII-raw byte ranges comprise all of Unicode

[Mattias Engdegård]

`rx' incorrectly considers character ranges between ASCII and raw bytes to 
cover all codes in-between, which includes all non-ASCII Unicode chars.
This causes (any "\000-\377" ?Å) to be simplified to (any "\000-\377"), which 
is not at all the same thing: [\000-\377] really means [\000-\177\200-\377] -- 
the transformation is normally made by the Emacs regexp engine. The two ranges 
are not contiguous on the character code level.

It's a sleeper bug that was awakened by my fixing bug#33205, so I'm to blame 
for not checking this.