[Bug demangler/80513] demangler walks past trailing nul in mangled name in a bunch of cases

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80513

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oops, no, that's not the right character to check!