Fix for browserify 7.0.2

Browserify writes transforms (and transforms added by plugins) through the build pipeline now. Resetting the bundler if it hasn't been bundled will create a new pipeline without any of those transforms. Additionally, calling `b.reset()` after bundling will create a new pipeline without the transforms. Calling `b.bundle()` again (rather than resetting) handles re-adding transforms automatically, but it would also add all of the recorded files again (which we handle with `b.require()`). The solution is to conditionally reset only if the bundler has been bundled, and to re-add any existing transforms manually after the reset.