Fixes OptionButton selection index being reset to zero at instanciation

[Alexander-Alekseev]

What we want to see is:

• Create OptionButton;
• Add items;
• Select desired item.

Till you are in GUI, the logic flow is correct. When you click Save Scene and/or Run Project the logic flow is:

• Create OptionButton (yes, save/run option creates a new one);
• Select desired item; <-- it fails because there are no items in popup as @bojidar-bg mentioned
• Add items. <-- when you have more than 1 item, this one selects item with index == 0

The root cause is that properties in OptionButton class placed in the order:

1. selected (_select_int method);
2. items (_set_items method).

Engine executes properties in this order once we save scene/run project.

This fix changes the order.

Bugsquad edit: fixes #10213

[akien-mga]

Thanks for the fix! I've merged it manually as 66c39b1 to add an explanatory comment and remove the extraneous merge commits. (See PR workflow for help on how to update your fork without generating such merge commits).