Fixing speedway so that it does not print a jump statement when not c…

…haining each term. (#359)

aerleon/lib/iptables.py

@@ -368,7 +368,7 @@ def __str__(self) -> str:
                                     )
                                 )
 
-        if self._POSTJUMP_FORMAT:
+        if self._POSTJUMP_FORMAT and self.chained_terms:
             ret_str.append(
                 self._POSTJUMP_FORMAT.substitute(filter=self.filter, term=self.term_name)
             )