Fix identification plots and display if something goes wrong in computation of Jacobians

Fixes #1860 (closed) Related !2050 (merged) Please also cherry pick for 5.2.

Identification toolbox ran into errors when the identification criteria based on moments (which are necessary for the strength diagnostics and plot_identification.m) could not be computed (e.g. order condition was not full-filled). This merge request now includes additional checks to make sure that the required objects are non-empty before displaying or plotting.