`sag` now fails when `.sackrc` does not exist

[ericsuh]

This error does not exist in 6a89205.

/home/vagrant/bin/sack: line 564: $sack__dev_null: ambiguous redirect
/home/vagrant/bin/sack: line 564: $sack__shortcut_file: ambiguous redirect
ERR: Error stat()ing:
ERR: Error opening directory : No such file or directory

/home/vagrant/bin/sack: line 577: [: ==: unary operator expected
/home/vagrant/bin/sack: line 579: [: ==: unary operator expected
Error: unsupported default editor specified in sack__default_editor

[ernstki]

… and this is partially my fault, because I broke install_sack.sh with my last pull request. How embarrassing.

I’m whipping up a new one (#35) with modifications that ensure that a ~/.sackrc is at least created on the first run. I can probably look at sack as well to at least give you a more helpful error message if the rcfile doesn’t exist.

[ernstki]

I think this was fixed by #35 (d5c61e5), and this issue could probably be closed.

Just weird that a reference to that PR doesn't show up here. 🤔

If @ericsuh is still having the problem, feel free to re-open and @-mention me, and I'll try to make things better.