Prevent NPE in NavTabScroller

    Bug: 5619924
    Monkey see, but Monkey don't do.

Change-Id: I807693425eea93c6cb8cf616f2ff7f8f0827026e
diff --git a/src/com/android/browser/NavTabScroller.java b/src/com/android/browser/NavTabScroller.java
index 0bfe185..c940bf5 100644
--- a/src/com/android/browser/NavTabScroller.java
+++ b/src/com/android/browser/NavTabScroller.java
@@ -241,6 +241,7 @@
     void snapToSelected(int pos, boolean smooth) {
         if (pos < 0) return;
         View v = mContentView.getChildAt(pos);
+        if (v == null) return;
         int sx = 0;
         int sy = 0;
         if (mHorizontal) {