"${#:+\e}" should evaluate to \e, not e

[Crestwave]

Required for #679. I haven't checked any manuals, but I think that backslashes in quoted + parameter expansion should only be interpreted if preceding a special character.

$ echo "${#:+\$}"
$
$ echo "${#:+\e}"
\e

osh$ echo "${#:+\$}"
$
osh$ echo "${#:+\e}"
e

[andychu]

Fixed. Thanks, great catch! All shells appear to agree on this except yash: there are 4 special characters within double quotes: $ " backtick \.