fix for pretty_generate throwing wrong number of arguments error

[CodyBriscoe]

Found this error to first appear in 2.11.0 as a breaking change in one of our codebases.

When State === opts is false, pretty_generate would eventually call generate with 3 arguments:
State.generate(obj, options, nil)

However if State === opts, it would originally try to call state.generate(obj) with only one argument. However, state just returns the State class itself JSON::Ext::Generator::State and expects 3 arguments.

This change aligns the behavior with the regular JSON.generate method to call opts.generate instead.

[byroot]

Oh, that's a dumb mistake. Could you add a regression test?

I can release the fix quickly.

[CodyBriscoe]

Sure thing, will have that up in a moment

[CodyBriscoe]

@byroot let me know if you want anything tweaked or added