Fix a clazy warning, like:
Don't call QVector::begin() on temporary [clazy-temporary-iterator]
Indeed, we may pass begin and end iterators for 2 different
instances of temporary vector (shared though).
In addition: use const iterators.
Change-Id: Iac1055d9fc226f1b48ca72ee4f3aab433addfe7f
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>