Ensure times at which chpi are fitted are valid samples (#8827)

* Ensure times at which chpi are fitted are valid samples

* SKip zero-length annotation

mne/chpi.py

@@ -943,8 +943,8 @@ def compute_chpi_amplitudes(raw, t_step_min=0.01, t_window='auto',
                 % (len(hpi['freqs']), len(fit_idxs), tmax - tmin))
     del tmin, tmax
     sin_fits = dict()
-    sin_fits['times'] = (fit_idxs + raw.first_samp -
-                         hpi['n_window'] / 2.) / raw.info['sfreq']
+    sin_fits['times'] = np.round(fit_idxs + raw.first_samp -
+                                 hpi['n_window'] / 2.) / raw.info['sfreq']
     sin_fits['proj'] = hpi['proj']
     sin_fits['slopes'] = np.empty(
         (len(sin_fits['times']),

mne/preprocessing/maxwell.py

@@ -478,6 +478,8 @@ def _run_maxwell_filter(
     logger.info(
         '    Processing %s data chunk%s' % (len(starts), _pl(starts)))
     for ii, (start, stop) in enumerate(zip(starts, stops)):
+        if start == stop:
+            continue  # Skip zero-length annotations
         tsss_valid = (stop - start) >= st_duration
         rel_times = raw_sss.times[start:stop]
         t_str = '%8.3f - %8.3f sec' % tuple(rel_times[[0, -1]])

mne/tests/test_chpi.py

@@ -495,6 +495,7 @@ def test_calculate_chpi_coil_locs_artemis():
     raw = read_raw_artemis123(art_fname, preload=True)
     times, cHPI_digs = _calculate_chpi_coil_locs(raw, verbose='debug')
 
+    assert len(np.setdiff1d(times, raw.times + raw.first_time)) == 0
     assert_allclose(times[5], 1.5, atol=1e-3)
     assert_allclose(cHPI_digs[5][0]['gof'], 0.995, atol=5e-3)
     assert_allclose(cHPI_digs[5][0]['r'],