New file behavior is a bit confusing

Nobody has claimed this yet.

When I click on a markdown link for a non-existent file and the "automatically create files for link targets" option is checked off, Mac Down will open a new, blank editor. Perfect. However, upon entering text into the blank editor, I receive a message that says this:

> The file cannot be found.
> You can duplicate this document and edit the duplicate. Only the duplicate will include your changes.

Also the editor is locked. I don't think this should be the behavior, but maybe I'm not understanding the use case you're supporting. I would like to begin editing, and then once the buffer is full of things that I want to save to that file, I should be able to File->Save and then the file will be created.

There is a work around. If I immediately File->Save with the buffer empty, it will create the file and I will be able to continue editing. However this work around, of saving a blank file, is pretty counter to any program I've used that's capable of doing a file safe. If this is not a necessary behavior I think it would be great if it were changed to align itself with the user experience of more common editors.

Start by reproducing the workflow in MacDown: open a markdown link for a missing file with automatic file creation disabled, type in the blank editor, and use File->Save. Trace the missing-file editor and save behavior; done means the new file can be edited and created on save without first saving an empty buffer.

Written by the indexing model from the issue text.