POINT_VARIANCE_THRESHOLD error on Solve Camera Pose

[K-Meech]

Sometimes when 'Solve Camera Pose' is clicked, the following error occurs from openCV:

ret, rvec, tvec, error = cv.solvePnPGeneric(
cv2.error: OpenCV(4.8.0) D:\a\opencv-python\opencv-python\opencv\modules\calib3d\src\sqpnp.cpp:242: 
error: (-215:Assertion failed) point_coordinate_variance >= POINT_VARIANCE_THRESHOLD 
in function 'cv::sqpnp::PoseSolver::computeOmega'

This is usually solved by placing more points, or removing ones that are poor matches. It would be good to catch this error, and provide an informative message to the user.

OpenCV code for reference: https://github.com/opencv/opencv/blob/748279d5f1026c265335c3ac5f0a56007f83a915/modules/calib3d/src/sqpnp.cpp#L242