Fix errors in re-observing properties for previously cleaned up weak references. [#441, #442]
Fix errors in re-observing properties for previously cleaned up weak references. [#441, #442]

MishaMykhalyuk/rivets,zongkelong/rivets,benderTheCrime/tiny-rivets,QAPInt/rivets,mikeric/rivets,GerHobbelt/rivets,jccazeaux/rivets,mikeric/rivets,QAPInt/rivets,altmind/rivets,nopnop/rivets,MishaMykhalyuk/rivets,altmind/rivets,MishaMykhalyuk/rivets,zongkelong/rivets,QAPInt/rivets,GerHobbelt/rivets,nopnop/rivets,GerHobbelt/rivets,re-clone/rivets,altmind/rivets,zongkelong/rivets,jccazeaux/rivets,re-clone/rivets,nopnop/rivets,mikeric/rivets,jccazeaux/rivets,re-clone/rivets