Enclose second arg to test with double-quotes

[ammgws]

Missed this in #59

On sway, when the screen is locked all containers lose focus and hence __done_get_focused_window_id returns a null value, which results in the following error when done runs:

test: Missing argument at index 2

~/.config/fish/conf.d/done.fish (line 45): 
    if test "$__done_initial_window_id" != (__done_get_focused_window_id)
      ^
in function '__done_is_process_window_focused'
    called on line 80 of file ~/.config/fish/conf.d/done.fish
in function '__done_ended'
in event handler: handler for generic event “fish_prompt”

(Type 'help test' for related documentation)

[franciscolourenco]

Thanks!