Radial recycling causes crash on cold start in 2D with core sources

[mikekryjak]

I have just started a simulation on a new grid and wanted to do it from scratch. I was only able to start the simulation without core sources and with everything turned down/off, as per the last time I did this with the MAST-U cases.

I just did some more testing and found that the case can be started from cold with all the bells and whistles (core sources present, final density and pressure settings, etc) if radial recycling is disabled.

This suggests there is likely a bug in recycling.cxx which causes an unphysical situation only at the very start of the solution.