mcx2json unable to export simulations of continuously-varying media

[fangq]

please see this post in the mailing list

https://groups.google.com/g/mcx-users/c/5XgJewedU2c

it can be reproduced using the muamus_float (2nd) simulation from https://github.com/fangq/mcx/blob/master/mcxlab/examples/demo_continuous_mua_mus.m