Vim errors destroy saved session

[dbarnett]

What steps will reproduce the problem?

1. Add throw "BOOM" to the top of your .vimrc
2. Launch a8 with sessions set to save
3. Open any file in the vim editor
4. Close a8
5. Launch a8
6. Close a8
7. Launch a8 a third time

What is the expected output? What do you see instead? The file you opened earlier should still be open in the vim editor, but vim will show no opened files after opening a8 the third time.

I think I've also seen some types of vim errors break restoring the session immediately, so that after launching a8 the first time with the error, you see red error text and no restored session.