Don't try to delete entries which no longer exist

[winstliu]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

Do not attempt to delete files/folders that no longer exist. This can happen when:

• The entry is deleted outside of Atom before "Move to Trash" is selected
• A folder and one of its children are both selected for deletion, but the parent folder is deleted first

Alternate Designs

None.

Benefits

Since the file no longer exists, we don't have to try deleting it! And hence no error will be shown.

Possible Drawbacks

This won't keep track of renames.

Applicable Issues

Couldn't find any.

Additional info: the existing spec to make sure error notifications were displayed was actually using this behavior to trigger the notification. I have rewritten it to spy on the actual trash method and return false from there, tricking Tree View into thinking that the operation failed.