fix: backward compatibility of to/from numpy (#455)

Author: alejoe91

src/probeinterface/probegroup.py

@@ -200,7 +200,10 @@ def from_numpy(arr: np.ndarray) -> "ProbeGroup":
         probegroup = ProbeGroup()
         for probe_index in probes_indices:
             mask = arr["probe_index"] == probe_index
-            probe_id = arr["probe_id"][mask][0]
+            if "probe_id" not in arr.dtype.fields:
+                probe_id = str(probe_index)
+            else:
+                probe_id = arr["probe_id"][mask][0]
             probe = Probe.from_numpy(arr[mask])
             probegroup.add_probe(probe, probe_id=probe_id)