Fix 3801 - Add ALEDummySign some width.

[hsanson]

Due to changes in NeoVim 0.5 the g:ale_sign_column_always configuration
stopped working.

This PR sets the ALEDummySign to a blank space so when g:
ale_sign_column_always is set we have a sign with 1 width allowing the
configuration to work as before.

• NeoVim issue: Recent commit adding support for 0-width signs breaks ALE plugin neovim/neovim#13635
• Superceds Fix ale_sign_column_always for Neovim 0.5 #3672
• Closes Sign gutter not opened by default in Neovim v0.5 #3801

[RobbieClarken]

I've confirmed this fixes the issue where g:ale_sign_column_always wasn't having any effect in neovim nightly (v0.6.0-dev+nightly-169-gd791274a9).

Unfortunately it introduces a small rendering issue where the first two cells on the first line are styled incorrectly:

This only happens if g:ale_sign_column_always is set to 1 and it happens for vim 8.2 as well as neovim nightly. It doesn't happen for vim or neovim without this patch.

My colorscheme is gruvbox-dark-hard from chriskempson/base16 but I've also confirmed the rendering issue happens with morhetz/gruvbox.

[hsanson]

@RobbieClarken thanks for testing. I was unable to see that artifact due to my colorscheme, good thing to have others check in their setups.

I have made a small modification, please let me know if it solves the rendering issue.

[RobbieClarken]

@hsanson That fixes the rendering in both vim and neovim. Everything looks to be working perfectly now. 👏