Wait for fingerprints to be removed (Partial fix).

This is a partial fix for b/27903189.
When we remove the lock screen and remove all fingerprints, wait for
them to all be removed before finishing the activity. This will let
the security screen accurately show how many fingerprints are available.

bug:27903189
Change-Id: I30908dbefb7a858f6d99e532841ed4ff894bfe62

src/com/android/settings/ChooseLockGeneric.java

@@ -648,9 +648,14 @@ public class ChooseLockGeneric extends SettingsActivity {
                                 mFingerprintManager.setActiveUser(UserHandle.myUserId());
                             }
                         });
-            }
+            } else {
+                // The removal callback will call finish, once all fingerprints are removed.
+                // We need to wait for that to occur, otherwise, the UI will still show that
+                // fingerprints exist even though they are (about to) be removed depending on
+                // the race condition.
                 finish();
             }
+        }
 
         @Override
         public void onDestroy() {