Property NOTIFY signal should be -1 for notification-less signals

[arnetheduck]

qmetaobject-rs/qmetaobject_impl/src/qobject_impl.rs

Line 293 in 81e9ad1

None => self.push_int(0 as u32),

sets the metadata to 0 for properties that don't have an associated notify signal - however, as can be spotted in generated files and from the dynamic metaobject generator, -1 would be the more appropriate value.