Fix NPE if draging again while animating

The animator cancel calling might cause surfaces released by our
implementation. Moving the cancel call before we make sure surface
is not null.

Fix: 230686609
Fix: 233159027
Test: Open animation scale setting and try drop then drag again
      divider quickly
Test: pass exising tests
Change-Id: I2e94f3ece3f211ceb15f380e4ee9322b8c27f8ac
Merged-In: I2e94f3ece3f211ceb15f380e4ee9322b8c27f8ac
(cherry picked from commit 99866c56)