Fix NPE in setActiveTab

    Bug: 5248939 5214748
    The second bug is actually different, and was not repeatable
    but the first case is now protected

Change-Id: I26f16ee3a828f6e9208c02cde89faa43a0423428
diff --git a/src/com/android/browser/BaseUi.java b/src/com/android/browser/BaseUi.java
index 17ba4d7..bce3257 100644
--- a/src/com/android/browser/BaseUi.java
+++ b/src/com/android/browser/BaseUi.java
@@ -247,8 +247,7 @@
         setShouldShowErrorConsole(tab, mUiController.shouldShowErrorConsole());
         onTabDataChanged(tab);
         onProgressChanged(tab);
-        boolean incognito = mActiveTab.getWebView().isPrivateBrowsingEnabled();
-        mNavigationBar.setIncognitoMode(incognito);
+        mNavigationBar.setIncognitoMode(tab.isPrivateBrowsingEnabled());
         updateAutoLogin(tab, false);
         if (web != null && web.getVisibleTitleHeight()
                 != mTitleBar.getEmbeddedHeight()