And use it from QgsVectorLayerFeatureIterator
References #472
The current implementation is really just a wrapper around distance()
but opens the door for future improvements
desirable.
By default these errors are logged to the console and in the QGIS UI.
But for some operations errors are expected and logging these just results
in noise.
For the c++ api dox this expands to "\c nullptr" (the
\c directive indicates a code literal value), and for sipify/Python
it expands to ``None`` (`` is sphinx annotation for literal values)
Makes for nicer dox for both c++ and Python!
