[OrPostingIterator] Fix nullptr handling
QVector::end()
iterator gets invalidated when QVector is modified via QVector::erase()
,
so don't store it.
I'm not even sure why the test worked in the first place, that should be undefined behavior.
For example, if vector ends with nullptr, the current code crashed with
ASSERT failure in QVector::erase: "The specified iterator argument 'aend' is invalid"
(modified test scenario for this particular case)