Print help text if no subcommand is provided

Change-Id: Id9abc3ab45af8b6e44904090e179ce67a3f45796
Reviewed-on: https://gerrit.libreoffice.org/2541Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>

logerrit

@@ -48,7 +48,7 @@ submit() {
 }
 
 case "$1" in
-	help|--help)
+	help|--help|"")
 		echo "Usage: ./logerrit subcommand [options]"
 		echo "simple and basic tool to interact with LibreOffice gerrit"
 		echo "subcommands:"