Bugfix crash when bilby_mcmc attempts to produce diagnostic histograms for parameters with infinte values
I ran into an error while testing that there would be fatal errors while producing these histograms when the parameters in question had some infinite values.
Naturally that's a bad thing on its own, but it should at least not cause the sampler to crash in the process, so this checks for that and simply doesn't plot them if infinite values are present.
