write_raw_bids shoudn't write stim channels to electrodes.tsv

[scott-huberty]

I suppose I will label this as a bug, as the current behaviour is inconsistent with the BIDS standard, per discussion in #1006

write_raw_bids shouldn't write stim channels to the electrodes.tsv sidecar file, because stim channels don't have associated electrodes.

I can amend the code in _write_electrodes_tsv, and submit a PR. I will suggest something like:

if ch['kind'] == FIFF.FIFFV_STIM_CH:
    continue

at the beginning of this for loop:

mne-bids/mne_bids/dig.py

Lines 140 to 152 in 54d50f6

	for ch in raw.info['chs']:
	if (
	np.isnan(ch['loc'][:3]).any() or
	np.allclose(ch['loc'][:3], 0)
	):
	x.append('n/a')
	y.append('n/a')
	z.append('n/a')
	else:
	x.append(ch['loc'][0])
	y.append(ch['loc'][1])
	z.append(ch['loc'][2])
	names.append(ch['ch_name'])

[hoechenberger]

+1 on fixing this, I like your proposal!

Edit:
I'd add a log message with severity DEBUG too

[scott-huberty]

Okay! included a logger.debug message and submitted a PR!