On finishing/terminating a thread, when processing posted events,
we need to consider QThread's own data instead of caller thread's data.
Otherwise we can get into unexpected situations such as double
destruction of an object, premature destruction, etc.
Fixes: QTBUG-103922
Pick-to: 6.4 6.3 6.3.1 6.2 5.15
Change-Id: Idf77221ebbaa0b150ee2d0c296b51829ae8dc30e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>