fix: initialize md_text in _parse_rss_type to prevent UnboundLocalError (#2164)

Author: smedavarapu1

packages/markitdown/src/markitdown/converters/_rss_converter.py

@@ -186,8 +186,9 @@ def _parse_rss_type(
         channel_title = self._get_data_by_tag_name(channel, "title")
         channel_description = self._get_data_by_tag_name(channel, "description")
         items = channel.getElementsByTagName("item")
+        md_text = ""
         if channel_title:
-            md_text = f"# {channel_title}\n"
+            md_text += f"# {channel_title}\n"
         if channel_description:
             md_text += f"{channel_description}\n"
         for item in items: