Do not fail in case secondary data not exists.

youtube_dl/extractor/facebook.py

@@ -354,7 +354,7 @@ class FacebookIE(InfoExtractor):
                 video_id, transform_source=js_to_json, fatal=False)
             video_data = extract_from_jsmods_instances(server_js_data)
 
-        tahoe_secondary_data = ''
+
         if not video_data:
             if not fatal_if_no_video:
                 return webpage, False
@@ -396,6 +396,8 @@ class FacebookIE(InfoExtractor):
                 data=tahoe_request_data,
                 headers=tahoe_request_headers, fatal=False
             )
+            if not tahoe_secondary_data:
+                tahoe_secondary_data = ''
                 
             tahoe_js_data = self._parse_json(
                 self._search_regex(