Allow empty commits when `uses_rpmautospec`
To avoid situations where the command `commit` by default does
commit when no change in repo is present.
Fixes: #677
JIRA: RHELCMP-11489
Merges: https://pagure.io/rpkg/pull-request/688
Signed-off-by: Jiri Kyjovsky <j1.kyjovsky@gmail.com>