Ignore unspeciffied interaces when getting service by interface

Hi, with current version I ran into trouble when getting a service, named with FQN of some interface. The service was provided by another abstract factory, but PHP-DI threw an exception in its AF, because it found that interface, but has no implementation mapped to it.
I had to override that behavior of PHP-DI to make canCreateServiceWithName method return FALSE in that case, instead of throwing an exception, and allow to pass the service resolution to other abstract factories that may provide that service.

If there is some simpler solution to determine, whether the interface can be injected by PHP-DI, or not, it woul be great.

Maybe we should implement some canCreate metohd to PHP-DI itself to be able to better determine, if we can create a service, without throwing/catching exceptions.

I'll try to provide some tests too