warning and stacktrace

In case SWT event is sent during doUpdateItem() we should run async
update to avoid RuntimeException from ColumnViewer.checkBusy().

Change-Id: Ic532ec0a2458eba2037dc741374454a896569e94
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>
(cherry picked from commit efda4d1cc8d31993d665965e278f46ac0d58f15c)