Fix the bug which occurs a fatal error when only one argument is given to debugf() and so on refs #434: Fatal error occurs when an object is given to debugf()
 Merge branch 'develop' into 'master'

Fix the bug which occurs a fatal error when only one argument given to debugf()

As title, fixed the bug.
It occurs under the following:

```
use \Log\Minimal;

$obj = new StdClass();
Minimal::debugf($obj);
```