fix: DragRect resizing when its size is zero

[JunkyoLee]

Previously, DragRect could not be resized if its current size was zero, which prevented users from initializing or adjusting the rectangle from a zero-size state.

Modified the logic to allow moving the rect only when either its width or height is non-zero

[Copilot]

Pull request overview

This PR fixes a usability issue where DragRect widgets could not be resized when initialized with zero width and zero height. The fix conditionally disables the center-point move handle when the rectangle has zero size, while keeping all corner and edge resize handles accessible.

Key Changes:

• Added is_movable check to disable center-point dragging when both dimensions are zero
• Improved variable scoping by moving b_rect declaration inside conditional blocks
• Maintained full resize functionality via corner and edge handles

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[brenocq]

Lovely!!

master:

Kooha-2025-12-03-07-37-00.mp4

dragrect_resizing:

Kooha-2025-12-03-07-35-44.mp4

Thanks for the minimal changes and for following conventional commits :)