fix various NPEs

    Bugs: 4597115
    	  4580514
	  4580511
	  4560889
	  4545346

    Monkey proofing nav screen;
    disabled pause/resume during scroll

Change-Id: I4e24b91fc0b6c008cb4e2df113316c0063f0c915
diff --git a/src/com/android/browser/NavTabView.java b/src/com/android/browser/NavTabView.java
index 061e024..f170b0f 100644
--- a/src/com/android/browser/NavTabView.java
+++ b/src/com/android/browser/NavTabView.java
@@ -198,7 +198,9 @@
 
     @Override
     public void onDetachedFromWindow() {
-        mWebView.setProxyView(null);
+        if (mWebView != null) {
+            mWebView.setProxyView(null);
+        }
     }
 
     private static void removeFromParent(View v) {