fix issue-923, error when no config file found

slither/utils/command_line.py

@@ -70,6 +70,11 @@ def read_config_file(args):
             logger.error(
                 red("Impossible to read {}, please check the file {}".format(args.config_file, e))
             )
+    else:
+        logger.error(
+            red("File {} is not a file or does not exist".format(args.config_file)),
+            yellow("Falling back to the default settings...")
+        )
 
 
 def output_to_markdown(detector_classes, printer_classes, filter_wiki):