If the subpath parameter to the git fetcher ends with a trailing '/',
bb.utils.prunedir() will be called on '/'...
Fixes [YOCTO #7620].
(Bitbake master rev: 380a3fb372c8b0a53dd7528562e6e7a222dc76ef)
(Bitbake rev: 7110055ab26d40e2a4e83956177b59a58e9cdcfd)
Signed-off-by: Anders Darander <anders@chargestorm.se>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>