avoid PHP warning message when checking non-existing disk file with func...

I use Patchwork when doing unit tests and event-driven tests with legacy code (where dependency injection was not implemented). There are at least two autoload functions registered, which causes some issue with Patchwork.

In case a file is loaded via the 2nd autoload function but not the 1st one, PHP function call stat() is going to trigger an E_WARNING error.

This pull request is to address the issue to avoid the E_WARNING error being sent out. Thanks