code: void endFinalizerGap(Env<GenContext> env) {
          if (env.info.gaps != null && env.info.gaps.length() % 2 == 1)
              env.info.gaps.append(code.curCP());
      }
docs: Mark end of gap in catch-all range for finalizer.
  @param env   the environment which might contain the finalizer
  (if it does, env.info.gaps != null).