Fixes NullPointerException while setting the bookmark flag

Added the condition to check the mUrl for null

CR-Fixed: 927089

Change-Id: I81aad169dee3911cd03b705c3f411b5f7aebb3b9
diff --git a/src/com/android/browser/Tab.java b/src/com/android/browser/Tab.java
index ebeeadf..7fafa03 100644
--- a/src/com/android/browser/Tab.java
+++ b/src/com/android/browser/Tab.java
@@ -1830,7 +1830,7 @@
             = new DataController.OnQueryUrlIsBookmark() {
         @Override
         public void onQueryUrlIsBookmark(String url, boolean isBookmark) {
-            if (mCurrentState.mUrl.equals(url)) {
+            if (TextUtils.isEmpty(mCurrentState.mUrl) || mCurrentState.mUrl.equals(url)) {
                 mCurrentState.mIsBookmarkedSite = isBookmark;
                 mWebViewController.bookmarkedStatusHasChanged(Tab.this);
             }