Fix issue where isDeleted incorrectly returned true…

[savetheclocktower]

…when a buffer is newly created and set to a path that does not yet exist on disk.

This is something I screwed up on #13. To track a buffer’s “deleted” state — meaning “is not currently backed by a file on disk, but was at one point” — we keep a didHaveFileOnDisk property and change it as needed.

In TextBuffer::load, I unconditionally set

this.didHaveFileOnDisk = true

because I suppose I thought that the load method would always be loading a file from disk. But there are use cases for calling load when the buffer’s file instance is set to a nonexistent path.

let someBuffer = TextBuffer.load('nonexistent.txt')

The above snippet creates a new buffer much the way it would if you'd simply said new TextBuffer — but it already knows where it will save once you ask it to save itself. So in TextBuffer::load (called by the static TextBuffer.load) we must set didHaveFileOnDisk based on whether the file actually exists instead of assuming true.

Easy to modify an existing spec to do a sanity-check here.

This is why pulsar#1588 is still in draft; this regression caused an autosave spec to fail. Gotta land this fix and then bump text-buffer again before that PR is ready to come out of draft.