Check the size of the covariance matrix wrt known number of parameters and act accordingly: - If it is empty, just fill a diagonal correlation matrix and issue a warning. - If it results from a failed first stage of a two-stage fit then the correlation matrix is padded with 1s and 0s for the parameters that were fixed in the first stage. closes #46

git-svn-id: svn+ssh://phab.hepforge.org/source/laurasvn/trunk@321 30227d83-a2f9-49e9-9e98-657c83b2c86a