re-add flag_secure to prevent showing content if app is locked

Signed-off-by: tobiasKaminsky <tobias@kaminsky.me>

src/main/java/com/owncloud/android/authentication/PassCodeManager.java

@@ -66,7 +66,7 @@ public final class PassCodeManager {
         this.preferences = preferences;
     }
 
-    public void onActivityCreated(Activity activity) {
+    private void setSecureFlag(Activity activity) {
         Window window = activity.getWindow();
         if (window != null) {
             if (isPassCodeEnabled() || deviceCredentialsAreEnabled(activity)) {
@@ -81,6 +81,8 @@ public final class PassCodeManager {
         boolean askedForPin = false;
         Long timestamp = AppPreferencesImpl.fromContext(activity).getLockTimestamp();
 
+        setSecureFlag(activity);
+
         if (!exemptOfPasscodeActivities.contains(activity.getClass()) && passCodeShouldBeRequested(timestamp)) {
             askedForPin = true;