1. Following condition is True on each iteration becuase -1 % 0xFF is 255 not -1

code = cv2.waitKey(100) % 0x100
if code != -1:
   break

this were resetting point position on each cycle not on key press as intended

2. Previous small bug were masking serious bug with matrix operation on matrices of incorrect size.
   As the result on 2nd iteration of internal cycle program has crushed.

   I have fixed it too, matrix operation was taken from examples/cpp/kalman.cpp where it looks like
   randn( processNoise, Scalar(0), Scalar::all(sqrt(KF.processNoiseCov.at<float>(0, 0))));
   which is something totally different from previous code here.

   Example behave as it should now, i.e. point moving by circle trajectory as in C++ example.

Fixed regression in cv::VideoCapture with gstreamer back end that prevented viewing of rtsp streams.