QmakeProject: Fix crash on unloading project while parsing

Callign applyAsyncEvaluate in the desctructor might lead to further
parses, which we don't want. So bail out early in applyAsyncEvaluate.

Task-number: QTCREATORBUG-13421
Change-Id: I776ff477363a3985ebc26e9160c58c2ab9c910b7
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
QmakeProject: Fix crash on unloading projects

The QmakeVfs needs to be deleted after all evaluations have been
canceled. Those are canceled in the destructors of the nodes, so
delete the nodes before deleting m_qmakeVfs

Task-number: QTCREATORBUG-13421
Change-Id: I5883f5b2daa6a13ef4facf9b9dccc125a069df94
Reviewed-by: Orgad Shaneh <orgads@gmail.com>