Fix startActivities may put activity in new task unexpectedly

Commit 591bf6 misplaced the setResultTo to the creation loop
of starters that leads to ActivityStarter#mSourceRecord is
always null. Then during startActivities, if an activity has
different task affinity from the previous, it will be put in
a new task unexpectedly.

Also avoid getting the modified component specified flag.

Bug: 141525305
Test: atest StartActivityTests#testStartActivitiesInNewAndSameTask
Change-Id: I237c9abff6ed9b0afab114e14d57c67692576033