Fix an issue where the top bubble might not be correct

Regression from ag/27145767 -- need to also clear the magnetized
object in the click listener (not just the touch listener like that
change does).

Test: manual - 1 add some bubbles
             - 2 expand the stack, select a different bubble
             - 3 open the overflow, add a bubble
             - 4 collapse the stack
             =>  verify the bubble added in (3) is at the top of the stack
Bug: 339711720
Change-Id: I2090e0a365df39542676d5a9d0b98c85450f760e