Fix: use valid_indices is not None

@karim

An array of valid_indices should be used if it is not None.

cal_tools/cal_tools/agipdlib.py

@@ -1162,7 +1162,7 @@ class AgipdCorrections:
         if np.count_nonzero(can_calibrate) == 0:
             return
         allcells = allcells[can_calibrate]
-        if self.valid_indices is not None:
+        if self.valid_indices is None:
             firange = np.arange(first_index, last_index)
         else:
             firange = self.valid_indices