Build Asset Bundles trys to move manifest even when no bundles were built

[hiroki-o]

Original report by Anthony DiPirro (Bitbucket: adipirro, GitHub: adipirro).

---

While setting up a project I ran into an issue where "Build Asset Bundles" trys to rename the manifest file even when no bundles were built. Since no bundles were actually built, no manifest file is generated and a FileNotFoundException is thrown.

This can be reproduced by configuring an asset bundle from an empty directory.

[hiroki-o]

Original comment by Hiroki Omae (Bitbucket: [Hiroki Omae](https://bitbucket.org/Hiroki Omae), ).

---

Thank you for reporting. I will look into the issue.