bash-completion.el (bash-completion-quote): Add case for empty string

[abo-abo]

I was just noticed I didn't PR this commit from some time ago. Here's how it changes the behavior:

;; Before:
(bash-completion-quote "")
;; => ""

;; After
(bash-completion-quote "")
;; => "''"

If I remember correctly, the intention is to fix the difference between bash completion and emacs-bash-completion.el. When TAB is issued with the last word being empty, bash completion passes that last empty string in the list, which emacs-bash-completion.el just has a shorter list with no empty string.

[szermatt]

Thank you!