Drop LockPatternView, migrate to system's provider

app/src/main/java/com/hippo/ehviewer/ui/MainActivity.java

@@ -143,7 +143,7 @@ public final class MainActivity extends StageActivity
     @NonNull
     @Override
     protected Announcer getLaunchAnnouncer() {
-        if (!TextUtils.isEmpty(Settings.getSecurity())) {
+        if (Settings.getSecurity()) {
             return new Announcer(SecurityScene.class);
         } else if (Settings.getShowWarning()) {
             return new Announcer(WarningScene.class);
@@ -161,7 +161,7 @@ public final class MainActivity extends StageActivity
     // Sometimes scene can't show directly
     private Announcer processAnnouncer(Announcer announcer) {
         if (0 == getSceneCount()) {
-            if (!TextUtils.isEmpty(Settings.getSecurity())) {
+            if (Settings.getSecurity()) {
                 Bundle newArgs = new Bundle();
                 newArgs.putString(SecurityScene.KEY_TARGET_SCENE, announcer.getClazz().getName());
                 newArgs.putBundle(SecurityScene.KEY_TARGET_ARGS, announcer.getArgs());