Fix check on empty shank ids

Author: alejoe91

src/probeinterface/probe.py

@@ -946,7 +946,7 @@ def from_dict(d: dict) -> "Probe":
         probe = Probe(ndim=d["ndim"], si_units=d["si_units"])
 
         shank_ids = d.get("shank_ids", None)
-        if shank_ids is not None and np.all(shank_ids == ""):
+        if shank_ids is not None and np.all([s == "" for s in shank_ids]):
             # backward compatible hack with previous version
             shank_ids = None