Increment loopLevel prior to emitting aboutToBlock()/awake() signals

Without this, any deferred delete actions that occur as a result of
these signals will not be processed until the main event loop exits.

This is triggered by the QtWayland server, which uses aboutToBlock() to
process internal events such as surface destruction.

This is most likely a problem with other dispatcher instances, but the scope of
this change cannot be to fix every platform at once, so the test is deliberately
marked QEXPECT_FAIL for everything except the glib dispatcher for now.

Done-with: Aaron Kennedy <aaron.kennedy@jollamobile.com>
Task-number: QTBUG-36434
Change-Id: I3fc143ad442c3a499d09f795355c155ad21b126d