Prevent uncaught class-not-found exceptions

[staabm]

analog #6159

[staabm]

after this PR there is only one remaining place where reflectionProvider->getClass() is called without a previous hasClass() call.

rector-src/src/Reflection/ReflectionResolver.php

Line 63 in a3f0b1f

return $this->reflectionProvider->getClass($className);

I don't see a way how this method could return gracefully in this case.
I guess we could e.g. add a return null case, but this would mean a BC break for this method.

not sure how important this method is and how often used in 3rd party packages

(but this is something to consider as a separate issue and should not block this PR here)

[samsonasik]

Thank you @staabm