Pass address of pointer, not value pf pointer

This request fixes ROOT 6 specific segfaults in four unit tests in CondCore packages, although the tests still fail later due to a different problem.
In two places in the code, the address of a pointer to the return value needed to be passed to FunctionWithDict::invoke().
Unfortunately, the value of the pointer was passed instead (missing '&').
Editorial comment:  I hate code that is not type safe.
This request also does some minor optimization by avoiding unnecessary ObjectWithDict::typeOf() calls, since the return value is already known.
Please merge this request as soon as convenient.