fix grid_base.is_inside_rect() logical

[lucyking]

By convention, points on the right and bottom edges are not included.

Hi @Hexadotz, According to classes/class_rect2.html, only points on right and button edge needs -Vector2(1, 1) operation.

[Hexadotz]

Thanks lucyking, but i remember there were problems checking the top left corner too as sometimes it won't count the place as valid even though it clearly is, especially when placing an item next to another.
Could you test it more to see if it still happen?

[lucyking]

tested on 4.2.2 and 4.3 there's no such issue.