Show help string when onEnrollmentHelp() is called

The help string is not shown when onEnrollmentHelp() is called
between onEnrollmentProgressChange() and mTouchAgainRunnable#run().
To fix this issue, showError() should be called.

Bug: 30274453
Test: manual - start enrolling fingerprint and move finger fast on the sensor

Change-Id: Ie604532940e40cca66dc54b56c3cb4b828a07987

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

@@ -33,6 +33,7 @@ import android.graphics.drawable.Drawable;
 import android.hardware.fingerprint.FingerprintManager;
 import android.os.Bundle;
 import android.os.UserHandle;
+import android.text.TextUtils;
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.animation.AnimationUtils;
@@ -264,7 +265,10 @@ public class FingerprintEnrollEnrolling extends FingerprintEnrollBase
 
     @Override
     public void onEnrollmentHelp(CharSequence helpString) {
-        mErrorText.setText(helpString);
+        if (!TextUtils.isEmpty(helpString)) {
+            mErrorText.removeCallbacks(mTouchAgainRunnable);
+            showError(helpString);
+        }
     }
 
     @Override