This seems like old `timevaryinggrowth` code

I think logmre used to include the mean logm level, but most recent implementation does not. I think this initialisation goes back to the previous implementation.

logm should be set by default as it is done for timevaryinggrowth = FALSE. logmre will be defaulted to 0.

This code creates problems when simulating time varying growth and might lead to bad fitting when fitting a model with time varying growth.