runvmec crashes if you try to load in a 2nd input file

[landreman]

This is the issue I mentioned in the biweekly VMEC zoom call just now.

I would like to be able to call vmec from an outside application using the runvmec function,
using several different input files in succession. However I find that when runvmec is called more than once with readin_flag set, it crashes with an allocation error.

Here is a minimal example that demonstrates the problem: https://github.com/landreman/vmec_multiple_readin