lib/oe/package_manager: avoid traceback with no packages
If you were using deb packaging, had buildhistory enabled and produced
an SDK that contained no packages in one of the sysroots (such as with
uninative-tarball) then the do_populate_sdk was failing with a python
traceback because there were no fields to split in the output line.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
