fix case when no files were commited in remote push trigger

The issue appears together with --intent-to-add flag for adding new
files. Original testing has been performed by having already added new
files, thus it passed all checks.

This commit also adds `commit_author` option which will allow to
overwrite the author.

tests/testresources/core/ahriman.ini

@@ -40,6 +40,7 @@ target = gitremote
 target = gitremote
 
 [gitremote]
+commit_author = "user <user@host>"
 push_url = https://github.com/arcan1s/repository.git
 pull_url = https://github.com/arcan1s/repository.git