Bug in RPROMPT alighnment

[Dan Neal <dan.r.neal@xxxxxxxxx>]

When a hyperlink is included in the RPROMPT, zsh mistakenly thinks the RPROMPT is longer than it actually is.  This results in the RPROMPT not being aligned all the way to the right but floats further to the middle.

A minimal .zshrc demonstrating the bug:

```

RPROMPT=$(eval "echo '\e]8;;http://example.com\aThis is a link\e]8;;\a'")

```

The hyperlink specification is here:

https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda

Please feel free to email me or cc me with any followup.