Do not show a duplicate error for the currently displayed error.

[heyltsjay]

Currently, showing multiple duplicate errors in a row will show the first, and then add the rest to the errorsToDisplay queue. As a result, the same error dismisses just to reveal many duplicates.

There are a few potential solutions.

1. Don't show error if error is already in errorsToDisplay
2. If error is already in errorsToDisplay move it to the front of the list.
3. Don't show error if error is currently being shown.

This PR is for option 3, but we can discuss the other options.