fix: [pystemon importer] fix base64 encoding

Author: Terrtia

bin/importer/abstract_importer.py

@@ -89,7 +89,7 @@ def create_message(self, obj_id, content, b64=False, gzipped=False, source=None)
         if not gzipped:
             content = self.b64_gzip(content)
         elif not b64:
-            content = self.b64(gzipped)
+            content = self.b64(content)
         if not content:
             return None
         if isinstance(content, bytes):