Only access existing prefix indexes when exluding paths.
Only access existing prefix indexes when exluding paths.

Only add core dependencies path exclusions in `AopComposerLoader` when they can indeed been found within the current `ClassLoader`, to avoid PHP notices in scenarios where Composer provides multiple `ClassLoader`s.

Replaces #263, to target 1.x branch.

goaop/framework,goaop/framework,lisachenko/go-aop-php,lisachenko/go-aop-php