Fix files unique rule

src/jflow/rules.py

@@ -202,6 +202,6 @@ class FilesUnique(SimpleRule):
                 sub_parameter = arg.replace(self.parameter_name + ">", "").replace("-", "_")
                 sub_parameter_obj = sub_parameters[sub_parameter][0]
                 if isinstance(sub_parameter_obj, InputFile) or isinstance(sub_parameter_obj, InputDirectory):
-                    all_files.append(value[0])
+                    all_files += value
         if len(set(all_files)) < len(all_files):
             self.error("Some files into '" + self.parameter_name + "' are given several times")
\ No newline at end of file