This allows the code to safely fall back to dumping the basehash data
if the taskhash data isn't present for some reason. We could effecitvely
obsolete the runtime option and use this approach instead exclusively.
(Bitbake rev: 5ace320ccc01f4e326f90b7ba060dcbff3380dca)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>