Copied errorCovPre to errorCovPost. This allows the correct behaviour of the…

Copied errorCovPre to errorCovPost. This allows the correct behaviour of the uncertainty to grow when there is missing data for each predict step.

modules/video/src/kalman.cpp

@@ -266,6 +266,7 @@ const Mat& KalmanFilter::predict(const Mat& control)
 
     // handle the case when there will be measurement before the next predict.
     statePre.copyTo(statePost);
+    errorCovPre.copyTo(errorCovPost);
 
     return statePre;
 }