fix setup of qbs object

evaluate("{}") is not just inefficient. It doesn't even return an
object.

Change-Id: Ieae5cd250c1d1b669f3b92a33d0fe42b3c5500ab
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>