fix to make VKalVrtCvtTool work with size 6 and 21 input error matrices
A covariance matrix is symmetric, so there would be 21 distinct elements. However, there's an option in the code to not compute the full covariance, but only the diagonal elements. In that case, we'd have 6 elements.
Currently, VKalVrtCvtTool would try to access all 21 elements of the covariance matrix and start accessing random memory. In my opinion, this is likely a bug as the code seems to be setup in a way to write only diagonal elements of the covariance matrix.
This MR covers both cases; input covariance matrix size 6 and 21 and gives SC FAILURE for all other cases.
Tagging @ssnyder .