Fix #3685: Prevent coin collection through solid weak blocks

[baltazarReis]

This PR fixes a bug where players could collect coins trapped inside a WeakBlock (like ice blocks) before the block was destroyed.

Added is_solid_block() method to WeakBlock to check its current state.

Modified Coin::collision to prevent collection if the coin's center is inside a solid WeakBlock.

Closes #3685

[MatusGuy]

Is this really necessary? Getting this information from the current collision group would be much more accurate and would not require this extra method.

Suggested change

	/** Check if this block is still solid (not destroyed) and blocking objects */
	inline bool is_solid_block() const { return state != STATE_DISINTEGRATING; }

[MatusGuy]

Without that extra method, it becomes easier to write this in a concise manner:

Suggested change

	if (weak_block.is_solid_block()) {
	const Rectf& block_bbox = weak_block.get_bbox();
	if (coin_center.x >= block_bbox.get_left() &&
	coin_center.x <= block_bbox.get_right() &&
	coin_center.y >= block_bbox.get_top() &&
	coin_center.y <= block_bbox.get_bottom()) {
	return ABORT_MOVE;
	}
	}
	if (weak_block.get_group() == COLGROUP_DISABLED)
	continue;
	if (weak_block.get_bbox().contains(coin_center))
	return ABORT_MOVE;