This is caused by the code point check function shared by ascii and
other 8bit charsets. It actually doesn't check the code point. Fix
it by adding seperate code point check function for ascii. Give user
a warning message in current build. Will reject such kind of input
in future.

Reviewed-by: Roy Lyseng <roy.lyseng@oracle.com>
Reviewed-by: Tor Didriksen <tor.didriksen@oracle.com>