fix .find when inverse is set

### Goal
`.find([1])` should return an Array of entries, even when a invese object is in memory already.

### Problem
`.find` was not returning an Array when, inverse object was in memory, and calling `find([1])` passing only one element.

### Solution
Dont call `.flatten` on args before passing to `find_by_scan` method, otherwise `expects_array` var will always be false.

[related #12359] => CI is red in there because we added a `:inverse_of` on `Firm.clients_of_firm`. which revealed this issue.