pass a pointer instead of a reference to initFrom()

msvc thinks that it's impossible to create a null reference (because
some language lawyer said so) and thus complains about our assert that
checks the reference's validity. work around by not dereferencing the
pointers we already have.

Change-Id: Ife2288d4187860105de12fdebc0e671e0159ace3
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
(cherry picked from qtbase/11161bbfadd0056466fc414ed659d08a4a0fe492)