Fix mistaken backreference in some titles

This should resolve #267

bdfr/file_name_formatter.py

@@ -45,7 +45,8 @@ class FileNameFormatter:
             if re.search(fr'(?i).*{{{key}}}.*', result):
                 key_value = str(attributes.get(key, 'unknown'))
                 key_value = FileNameFormatter._convert_unicode_escapes(key_value)
-                result = re.sub(fr'(?i){{{key}}}', key_value, result,)
+                key_value = key_value.replace('\\', '\\\\')
+                result = re.sub(fr'(?i){{{key}}}', key_value, result)
 
         result = result.replace('/', '')
 

bdfr/tests/test_file_name_formatter.py

@@ -303,6 +303,7 @@ def test_multilevel_folder_scheme(
     ('test😍', 'test😍'),
     ('test😍 ’', 'test😍 ’'),
     ('test😍 \\u2019', 'test😍 ’'),
+    ('Using that real good [1\\4]', 'Using that real good [1\\4]'),
 ))
 def test_preserve_emojis(test_name_string: str, expected: str, submission: MagicMock):
     submission.title = test_name_string