[edfscan][guess_index_frm_file_name] manage the case part1 is None

tomoscan/esrf/edfscan.py

@@ -328,7 +328,10 @@ class EDFTomoScan(TomoScanBase):
                 part_2 = None
 
             if part_2 is None:
-                return int(part_1)
+                if part_1 is None:
+                    return None
+                else:
+                    return int(part_1)
             else:
                 return float(part_1) + part_2
         else: