Fix YAML deserialization of anonymous structs

`DelayedJob` makes freedom patches of `Psych`'s `resolve_class` method.
It misses to guard this method from empty class names.

`Psych` does it:
https://github.com/tenderlove/psych/blob/2c644e18/lib/psych/class_loader.rb#L25

While deserializing an anonymous struct the class name is an empty
string (`""`). Constantizing an empty string resolves to `Object`.

This leads to this error:

    #<NoMethodError: undefined method `members' for #<Object:0xXXXXXXX>>

After this commit deserializing anonymous structs works again.