tst_dialogs: QTRY_ on the expression (spyVisibilityChanged.count) not the variable.

We only assign to the variable once, so the value may not change in time.

Change-Id: I54ac7faad60d3984bfde4606aaf7e30a2340ba3e
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
tst_dialogs: verify that rootObject is valid

if there's an error during loading, it's much easier to spot if this fails
rather than crashes.

Change-Id: If0106729e18768819da8a877959a095398af8547
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>