Don't show previews in the app switcher by default

res/xml/preferences_app_protection.xml

@@ -40,7 +40,7 @@
             android:dependency="pref_timeout_passphrase" />
 
         <org.thoughtcrime.securesms.components.SwitchPreferenceCompat
-            android:defaultValue="false"
+            android:defaultValue="true"
             android:key="pref_screen_security"
             android:title="@string/preferences__screen_security"
             android:summary="@string/preferences__disable_screen_security_to_allow_screen_shots" />

src/org/thoughtcrime/securesms/util/TextSecurePreferences.java

@@ -826,7 +826,7 @@ public class TextSecurePreferences {
   }
 
   public static boolean isScreenSecurityEnabled(Context context) {
-    return getBooleanPreference(context, SCREEN_SECURITY_PREF, false);
+    return getBooleanPreference(context, SCREEN_SECURITY_PREF, true);
   }
 
   public static boolean isLegacyUseLocalApnsEnabled(Context context) {