The docs claim that QThreadPool always creates at least one thread.
However, the user can (usually by mistake) request zero or a negative
number of threads.
The maxThreadCount() function is simply returning the value, that was
requested by the user.
Since it's a public API, it is used in several places in QtConcurrent,
where it is assumed that the value is always positive. This can lead
to a crash if the user sets zero as a maxThreadCount.
Update all such places with std::max(maxThreadCount(), 1).
Prefer this approach over changing the return value of
maxThreadCount(), because its behavior is documented and tested.
Amends 885eff0537.
Fixes: QTBUG-120335
Pick-to: 6.7 6.6 6.5 6.2
Change-Id: Id3b2087cec7fbc7a2d42febca6586f2dacffe444
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
936e72d180