Filename or path using in comment is not validated

The command below falsely succeeds, even though the filename or path is invalid:
`git appraise comment -f missspelled.go -m 'some message'`

These comments seem to end up in the object referenced by .git/refs/notes/devtools/discuss and cause an error when listing with:

``` bash
git appraise show
> comments (2 threads):
> ... comment 1 ...
> fatal: Path 'missspelled.go' does not exist in ''
```

All comments, including the bad one, can be seen in the `--json` output.

It would also be nice to have guidance on editing/amending comments before pushing, since naively using `git notes remove ` does not appear to work(?)

In the meantime I discovered that it was possible to checkout the comments into their own branch and remove the problem comment using`git rebase --interactive`:

``` bash
git checkout -B comments refs/notes/devtools/discuss
git rebase -i HEAD~2
drop the commit, and manually fix the merge after git rebase --continue
git update-ref refs/notes/devtools/discuss comments
git checkout master
git branch -D comments
```