CloudViewer: addOrUpdateFrustum doesn't show correctly the actual frustum (with cx/cy offsets)

[matlabbe]

The problem with the current way to display it is that cx/cy are assumed to be exactly at the center of the image, which often are not, so the frustum shown is the ideal straight frustum based on field of view.

Similarly to jsk camera info display using image_geometry::PinholeCameraModel::projectPixelTo3dRay to find the 4 corners of the frustum, we could use internal CameraModel::project() with depth=1 (or actual max distance of the frustum) to get the four corners:

rtabmap/corelib/src/CameraModel.cpp

Lines 766 to 773 in 1dadd50

	void CameraModel::project(float u, float v, float depth, float & x, float & y, float & z) const
	{
	if(depth > 0.0f)
	{
	// Fill in XYZ
	x = (u - cx()) * depth / fx();
	y = (v - cy()) * depth / fy();
	z = depth;