Fix NPE

 Bug: 3299384
 Added missing null check.

Change-Id: Ib26135c6f0d743c6cda34bb1b2df6079f7851e72
diff --git a/src/com/android/browser/Controller.java b/src/com/android/browser/Controller.java
index b7a39a2..6d92ffd 100644
--- a/src/com/android/browser/Controller.java
+++ b/src/com/android/browser/Controller.java
@@ -1898,7 +1898,7 @@
 
         // Only update thumbnails for web urls (http(s)://), not for
         // about:, javascript:, data:, etc...
-        if (Patterns.WEB_URL.matcher(url).matches()) {
+        if (url != null && Patterns.WEB_URL.matcher(url).matches()) {
             new AsyncTask<Void, Void, Void>() {
                 @Override
                 protected Void doInBackground(Void... unused) {