The computed nesting level (which row an event to show in) was solely
based on begin+end events and "complete" events were ignored.
Compute the rows afterwards, similar to the "parent" computation that
the timeline model already does. Find the first row that is free,
and use that for the row of the item.
Change-Id: I890138c10f5038508da9b286b35d7bcfdf0ab64d
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>