g_object_get_property: Clarify meaning of G_TYPE_INVALID
g_object_get_property: Clarify meaning of G_TYPE_INVALID

"Uninitialized value" is partially correct, since it has not been
initialized with a type, but it's more precise to say
"zero-initialized value". It is still a programming error to pass a
pointer to uninitialized memory with arbitrary contents as the value.

Signed-off-by: Simon McVittie <0e1aea601907c1a85c2dc96e5ea37e23c58d2e9b@collabora.com>

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib