Fix ArrayIndexOutOfBoundsException after allowing reorder

Fixes: 378795050

Test: HeadsUpManagerPhoneTest

Test: send delayed HUN, open shade, close shade to allow reorder
      and removeEntry
      => no exception

Test: send delayed HUN, open shade, manually swipe dismiss HUN to
      removeEntry
      => entry removed from mEntriesToRemoveWhenReorderingAllowed,
         no memory leak

Flag: com.android.systemui.notification_avalanche_throttle_hun
Change-Id: I31e74a524dcf406c2c01b4ea524ff757c7726dc1