Consume error thrown when autosaving file without name
Consume error thrown when autosaving file without name

Summary: Fixes #142. An issue existed where opening vim without a file
path and then navigating away (with autosave turned on) resulted in an
error being thrown. Now, this error is caught and consumed and not
propagated to the user.

Test Plan:
1) Started up a vim instance without a file path.
2) Created a second tmux pane.
3) navigated to tmux pane with vim
4) entered insert mode and wrote some gibberish
5) navigated away from the tmux pane containing the vim instance
6) no error message was shown to me

christoomey/vim-tmux-navigator