lib/oe/reproducible: Fix error when no git HEAD
Fixes an error that occurs when attempting to get the timestamp of the
latest commit when there is no HEAD in the git repository. The easiest
way to trigger this condition is to use the 'subdir=' option when
specifying a 'git://' SRC_URI.
Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit
a64caca5b5dbe4a76acd0b5709b2c3e75b245863)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
