🐛(backend) prevent regex from matching empty string

Rework regex pattern to exclude empty string matches since
url_encoded_folder_path is optional.

Add additional test cases covering edge cases and failure
scenarios to improve validation coverage
and prevent false positives.

src/backend/core/recording/event/parsers.py

@@ -86,7 +86,7 @@ class MinioParser:
 
         # pylint: disable=line-too-long
         self._filepath_regex = re.compile(
-            r"(?P<url_encoded_folder_path>(?:[^%]+%2F)*)?(?P<recording_id>[0-9a-fA-F\-]{36})\.(?P<extension>[a-zA-Z0-9]+)"
+            r"(?P<url_encoded_folder_path>(?:[^%]+%2F)+)?(?P<recording_id>[0-9a-fA-F\-]{36})\.(?P<extension>[a-zA-Z0-9]+)"
         )
 
     @staticmethod

src/backend/core/tests/recording/event/test_parsers.py

@@ -129,8 +129,11 @@ def test_validate_invalid_filetype(minio_parser):
 @pytest.mark.parametrize(
     "invalid_filepath",
     [
-        "invalid_filepath",
+        "invalid_filepath",  # totally invalid string
         "recording/46d1a121-2426-484d-8fb3-09b5d886f7a8.ogg",
+        "recording/46d1a121-2426-484d-8fb3-09b5d886f7a8",  # missing extension
+        "46d1a121-2426-484d-8fb3-09b5d886f7a8",  # missing url_encoded_folder_path and extension
+        "",  # empty string
         "recording%2F46d1a1212426484d8fb309b5d886f7a8.ogg",
     ],
 )