ft_electroderealign with cfg.method='headshape' does not lead to proper alignment

[johaenns]

Describe the bug
ft_electrode_realign in "headshape" mode does not properly fit the electrodes to the head surface but shifts them towards the middle of the head.

To Reproduce

1. Run ft_electroderealign with cfg.method='headshape'

Expected behavior
Electrode positions get fit to the provided headshape with rigid body transformation.

Screenshots

Environment and versions (please complete the following information):
I assume any.

Additional context
Replacing line 58 of ft_warp_error.m by

dist = mean(abs(el(:,4)));

seems to fix the problem.