fix: crash when logging ip if roundup-server times out

Under some conditions (seen in production, no reproducer), if
connection timed out, there is no headers attribute
RoundupRequestHandler.

Check for headers attr before accessing self.headers.

Author: rouilj

roundup/scripts/roundup_server.py

@@ -542,7 +542,9 @@ def address_string(self):
         """
         from_forwarded_header=""
         forwarded_for = None
-        if 'X-FORWARDED-FOR' in self.headers:
+
+        # if connection timed out, there is no headers property
+        if hasattr(self, 'headers') and ('X-FORWARDED-FOR' in self.headers):
             forwarded_for = re.split(r'[,\s]',
                                      self.headers['X-FORWARDED-FOR'],
                                      maxsplit=1)[0]