Do not leak active/all strings in format_loop_windows; from Huihui Huang

in GitHub issue 4898.

format.c

@@ -4429,6 +4429,9 @@ format_loop_sessions(struct format_expand_state *es, const char *fmt)
 		free(expanded);
 	}
 
+	free(active);
+	free(all);
+
 	return (value);
 }