Avoid launching dialogs twice from double-clicking a preference.

Bug: 6500628

Only create the dialog if another one doesn't already exist.

Change-Id: Ie9be06a58c369299bcb67526e668785e6735a307

Author: Amith Yamasani

core/java/android/preference/DialogPreference.java

@@ -261,6 +261,8 @@ protected void onPrepareDialogBuilder(AlertDialog.Builder builder) {
 
     @Override
     protected void onClick() {
+        if (mDialog != null && mDialog.isShowing()) return;
+
         showDialog(null);
     }