Bug with git worktrees and git init

Hi,

I've been using multiple worktrees for months without issue (it's a great feature, thanks), until recently when I wanted to add hooks to them. So, when I added a template for the hooks, everything was fine until I did a git reset --hard in the original repo which both applied those changes to the other worktrees' working tree (the files on disk), and made my master branch kinda lose it's connection to the remote/think it was a kinda bare repo.

To reproduce this:

``` mkdir source-repo cd source-repo git init touch foo git add foo git commit -m 'Add foo' git worktree add ../worktree # which also creates a new branch 'worktree' touch bar git add bar git commit -m 'Add bar' cd ../worktree git init cd ../source-repo git reset --hard master cd ../worktree git status # Suddenly `bar` has appear the working tree and is not tracked ```

I don't really now what is up with this, but I did notice that it is the last worktree in which git init has been run that is affected. I only ran git init to copy the hooks from the template, but if that is not something you should do in a worktree then a check would have been nice.

Thanks for this awesome tool, and I hope this helps Max Nordlund