Width of popup_dialog() depends on wrap and showbreak values and exceeds window width

[bfrg]

Describe the bug
The popup window returned by popup_dialog() is drawn wider than it needs to be. The window width depends on the number of characters in showbreak.

To Reproduce

1. Run vim --clean tmp.vim -c "source tmp.vim"

" tmp.vim
let &showbreak = '+++'

function! Popup_dialog_cb(id, result) abort
        echo a:result ? "YES" : "NO"
endfunction

call popup_dialog(['Do some action? (y/n)'], {
        \ 'filter': 'popup_filter_yesno',
        \ 'callback': 'Popup_dialog_cb'
        \ })

2. The more characters are added to showbreak, the wider the popup dialog window gets, and eventually exceed the window width. Only by passing the popup window option {'wrap': v:false} to popup_dialog() will draw the dialog correctly.

Expected behavior
The width of the dialog window should not be drawn wider than the text displayed inside it.

Screenshots

let &showbreak = '+'

let &showbreak = '++'

let &showbreak = '+++'

let &showbreak = '+++'`
" Pass {'wrap': v:false} to popup_dialog()

Environment

• Vim version 8.1.1714
• Gentoo Linux
• xfce4-terminal