QtConcurrent::blockingMapped behavior changed since Qt5 if the output container does have a non-explit size c'tor

Hi all,

after switching from Qt5 to Qt6 QtConcurrent::blockingMapped produced wrong results for me when using it with an output container that lacked an explicit keyword.

The attached code snipped illustrates the case.

Without the explicit, the blockingMapped overload creates the output container with "OrderedReduce" as size parameter so the result has finally three elements instead of one.

The attached code example will work without error. To reproduce the issue you need to remove the explicit in line 55. Without the explicit you can make the example work again when using blockingMappedReduced instead as in line 87 instead.

Not sure if this is a bug in Qt since the explicit should be there in reasonably written container code, but as this was quite difficult to track down, I wonder if the overall situation could be improved. 

Best regards,

Maxim