fix: Calling db.KeyHelper with None raises a unhandled `NotImplem…

…entedError`

See https://github.com/viur-framework/viur-datastore/blob/45deae60afad6699a518ab88ab0ead3771926376/src/viur/datastore/utils.py#L92

Discovered during testing of viur-framework#1267

src/viur/core/skeleton.py

@@ -1098,7 +1098,7 @@ def read(
 
         try:
             db_key = db.keyHelper(key or skel["key"], skel.kindName)
-        except ValueError:  # This key did not parse
+        except (ValueError, NotImplementedError):  # This key did not parse
             return None
 
         if not (db_res := db.Get(db_key)):