Fix a 'memory leak'

Realistically, this memory will be reclaimed by the OS when we return
here. Regardless, we do a similar cleanup above if an exec() function
fails, and having the free here makes our tooling slightly happier.

Complained about by the static analyzer

Bug: None
Test: Ran the analyzer. It no longer complains about this leak.
Change-Id: Ia7107c585cc38fef8bd7c59d85ff896b04e93658