Catch exception when ViewRoot's surface is not valid.
Bug #3399426

Change-Id: Id4e0b8714c9520c4e84e81c2978752d46c912b6b
diff --git a/core/java/android/view/ViewRoot.java b/core/java/android/view/ViewRoot.java
index 41fc6c6..b21af41 100644
--- a/core/java/android/view/ViewRoot.java
+++ b/core/java/android/view/ViewRoot.java
@@ -1537,6 +1537,7 @@
                 int top = dirty.top;
                 int right = dirty.right;
                 int bottom = dirty.bottom;
+
                 canvas = surface.lockCanvas(dirty);
 
                 if (left != dirty.left || top != dirty.top || right != dirty.right ||