ANSI undo command deleting user changes

[matt1003]

Description: When executing the undo ansi command on an non-ansi file there is a potential for the user's previous changes to be delete. This occurs because the ansi plugin blindly uses the sublime text undo command to restore deleted escape codes; however if no escape codes have been deleted this will result in the user's previous changes being deleted.

Reproduce Issue:

1. Open a new file.
2. Insert text to the file.
3. Set the syntax to "ANSI" via the sublime text menu.
4. Set the syntax back to "Plain Text" via the sublime text menu. (note: the inserted text will be deleted)

Potential Solution: We should probably double check view.command_history() before invoking the sublime text undo command to ensure that we are undoing what we think we are undoing.

[jakkubu]

Well, I couldn't reproduce it now. Is it still an issue?

[matt1003]

I'm am still able to reproduce the issue with the same steps; just tested it with commit 143a6f8.