rl_message with invisible prompt chars in C locale

[Grisha Levit]

With LC_ALL=C, invisible characters in the prompt sometimes cause
incorrect redisplay when adding or clearing a message with a line
that's longer than the screen width.

Doesn't happen with every arbitrary text but a reliable reproducer is
to overflow the screen width with the same character, then type ^R.

printf -v s '%*s' $COLUMNS
PS1='\[\e[31m\]$\[\e[0m\] ' LC_ALL=C bash --norc -in <<<${s// /.}$'\cR'
$ ....................arch)`': .................................................
..