fix: Validate file only when file type is set to custom (#11036)

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/factories/file_factory.py

     ):
         return False
 
-    if config.allowed_file_extensions and file_extension not in config.allowed_file_extensions:
+    if (
+        input_file_type == FileType.CUSTOM
+        and config.allowed_file_extensions is not None
+        and file_extension not in config.allowed_file_extensions
+    ):
         return False
 
     if config.allowed_file_upload_methods and file_transfer_method not in config.allowed_file_upload_methods: