Fix bug #9429: no validate featureIds using all feature collection

This patch fixes bug http://hub.qgis.org/issues/9429

Any selection of features in QGIS calls to 'QgsVectorLayer::setSelectedFeatures' and from this commit (https://github.com/qgis/QGIS/commit/39fab67e602aaa8be7e561a50b40ab7c38914258) it loads all featureIds even when none features were selected.

When the layer has many features, it is a big bottleneck!

I think that this verification is unneccesary in most of situations because of selections become from a 'QgsFeatureIterator fit = getFeatures(...)' calls.