Does not respect fillchars setting

[jakestrahm]

in my case set fillchars=fold:\

Reproduce:

1. alter fillchars settings e.g. set fillchars=fold:\
2. observe change
3. install readablefold.vim
4. observe reversion of fillchars setting

[lambdalisue]

I have no idea about fillchars so please explain what is the issue more clearly.