sstate.bbclass: Make sure we don't have an empty fixmepath file
Jason Wessel noticed that a package without any fixmepath entries would
generate a sed warning about no input files. This patch resolves that
by ensuring that an empty fixmepath file never gets written into the
sstate archive. Also we avoid a second message by only doing xargs if
we got input.
Signed-off-by: Mark Hatle <mark.hatle@windriver.com> Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
