Use existing moduleName object for IIFE and UMD if present

[krzksz]

Hey!
Right now rollup seems to reset module namespace every time the file is executed as seen in this example((this.myBundle = {})). This is problematic when you have multiple packages that should exist in common namespace inside window object, but some of them are lazy loaded when rarely needed. In this situation the variable will be cleared every time dynamic bundle is included.

The solution would be to slightly change the code so the generated piece would look like: (this.myBundle = this.myBundle || {}).