Fix (or separate) script for analysing systems when boostrapping fails

[IAlibay]

When you have too few ligands available, calculation of correlation metrics in cinnabar will fail, see: OpenFreeEnergy/cinnabar#124

The easy fix here is to avoid calculating correlation metrics when this happens.

We should ammend the plotting script to optionally skip calculating these metrics, or if necessary provide a separate script.

[IAlibay]

Here is the alternative plotting script we used in these cases.

plot_results.zip