Work around errors from empty responses in calibration_client

src/cal_tools/calcat_interface.py

@@ -236,6 +236,9 @@ class CalCatApi(metaclass=ClientWrapper):
         )
 
         if not resp["success"]:
+            if resp["status_code"] == 200:
+                # calibration_client turns empty response into an error
+                return []
             raise CalCatError(resp)
 
         return resp["data"]