Fix StringIndexOutOfBoundsException in PackageManagerService

The method packageManagerService.getNextCodePath(String oldCodePath,
String prefix, String suffix) threw StringIndexOutOfBoundsException if
oldCodePath does not contain prefix, and prefix is longer than
oldCodePath, or if the preix and suffix overlap.

Fixes http://b/issue?id=2404232

Change-Id: Ib8abb16f8bfd08f607476d9289f46d170c43a076