QValueSpaceSubscriber connected to undefined RProperty doesn't emit contentsChanged() signal

Steps to reproduce:
1. Create QValueSpaceSubscriber with path mapped to undefined RProperty.
2. Verify that QValueSpaceSubscriber was successfully connected.
3. Publish some value on path observed by QValueSpaceSubscriber with QValueSpacePublisher.
4. Verify the count of contentsChanged() signals emitted by QValueSpaceSubscriber created in step 1.

Currently no signals are emitted, although QValueSpaceSubscriber::isConnected() returns true. It's misleading and not consistent with Symbian RProperty behavior.

I propose that for all platforms that doesn't support subscribing to undefined path, QValueSpaceSubscriber::isConnected() should return false if QValueSpaceSubscriber's path is set to undefined path.

I've attached test project that demonstrates the issue.