Don't need to authenticate fingerprint when the fingerprint list is empty.

Enter into the fingerprint list screen and can authenticate fingerprint still when the list is empty.
Test: manual - enrolling some fingerprints and remove all fingerprintd, touch the fingerprint touch panel and no response.

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

@@ -275,7 +275,8 @@ public class FingerprintSettings extends SubSettings {
         }
 
         private void retryFingerprint() {
-            if (mRemovalSidecar.inProgress()) {
+            if (mRemovalSidecar.inProgress()
+                    || 0 == mFingerprintManager.getEnrolledFingerprints(mUserId).size()) {
                 return;
             }
             if (!mInFingerprintLockout) {