Fix SubjectEphy when only a single time point

Author: EtienneCmb

frites/dataset/suj_ephy.py

@@ -168,7 +168,7 @@ def __new__(self, x, y=None, z=None, roi=None, times=None, agg_ch=True,
         # __________________________ Sampling rate ____________________________
         # infer the sampling frequency (if needed)
         if sfreq is None:
-            if times is not None:
+            if (times is not None) and (len(times) >= 2):
                 sfreq = 1. / (times[1] - times[0])
             else:
                 logger.warning("Impossible to infer the sampling frequency. "