core: Add missing initialisation of NoteDetails member
core: Add missing initialisation of NoteDetails member

Otherwise it’s implicitly initialised to null, which causes assertion
failures in the tests later on (it’s a state the rest of the code in
NoteDetails does not expect).

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

GNOME/folks,pwithnall/folks,GNOME/folks,pwithnall/folks,pwithnall/folks,GNOME/folks