There are two places where we are only interested in the mapping of
proxy to source sort column, rather than the full mapping. Creating the
full mapping is rather expensive as it iterates all rows and columns and
allocates a large number of objects. Just figuring out the n-th accepted
column can be much cheaper.
Fixes: QTBUG-41659
Change-Id: I7ea914cb695518b4d47cdc3ad67c7786380d8709
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>
a7df98a9a7