Error in empty repos

[DivineDominion]

It's obvious that magit-todo's can't to anything in an empty repo :) Since we get error in process sentinel this sounds like an unhandled case so far, though.

I just created a new repo via magit-init:

error in process sentinel: Wrong type argument: (or eieio-object cl-structure-object oclosure), nil [2 times]
error in process sentinel: magit-todos--async-when-done: magit-todos--async-when-done: Process "magit-todos--scan-with-rg" failed with exit code 2.  Output:"rg: No files were searched, which means ripgrep probably applied a filter you didn't expect.
Running with --debug will show why files are being skipped.
"

[alphapapa]

Yes, this is a duplicate of #167. Since a git repo isn't likely to stay empty, handling this case isn't important to me. But patches are welcome.