Fix some bugs

[aznhe21]

This PR fixes these bugs:

1. Running :HopVerticalAC when the cursor is on an empty line will print "col value outside range".
2. Running :HopVerticalMW when there is a floating window will print Invalid buffer id: N.
3. A potential issue that could cause "Not allowed to change text or change window".

[uplus]

I had this problem with HopLineStartAC in my environment.
This PR fixed it! Thanks!

1. Running :HopVerticalAC when the cursor is on an empty line will print "col value outside range".

[hadronized]

Can you document your changes? The plugin starts to become a mess with all the changes in the PRs trying to fix that problem, I will probably refactor all of that in a couple of days and I need to understand exactly what does what.

[aznhe21]

Sorry for the late reply. I have added comments about the changes. Please check it out.

[FelipeLema]

I'm using this branch and it seems to fix #335 👍🏾

[chaudry-786]

Any progress on this?

[aznhe21]

I'm waiting (for over a month!) for a review.
@phaazon Please confirm and merge.

[snaveevans]

@phaazon any chance this could get reviewed and merged?