Don't pass in empty arg to dex2oat.

We would occassionally pass in an empty arg "" instead of a NULL.
This caused problems since dex2oat isn't made to handle empty args.

(cherry picked from commit f53dbfeda39c290ed67b0682d559a80cb42ceb79)

Change-Id: Ia2d60b895391bf83b5d250c20ddb8a4917d347a6
1 file changed