Fix fingerprint enrolling bug.

This fixes a bug where rotating the device would call post_enroll()
too early, thus invalidating the current session.

Fixes bug 22708390

Change-Id: Ib4a334b50c16630b4fe4b451f6019d41225b2011

src/com/android/settings/fingerprint/FingerprintSettings.java

@@ -451,11 +451,13 @@ public class FingerprintSettings extends SubSettings {
         @Override
         public void onDestroy() {
             super.onDestroy();
+            if (getActivity().isFinishing()) {
                 int result = mFingerprintManager.postEnroll();
                 if (result < 0) {
                     Log.w(TAG, "postEnroll failed: result = " + result);
                 }
             }
+        }
 
         private Drawable getHighlightDrawable() {
             if (mHighlightDrawable == null) {