Avoid NPE in when calling isSearching

Got this in recent build:
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean org.wikipedia.page.PageActivity.isSearching()' on a null object reference
at org.wikipedia.page.PageViewFragment.onCreateOptionsMenu(PageViewFragment.java:145)
at android.support.v4.app.Fragment.performCreateOptionsMenu(Fragment.java:1868)
at android.support.v4.app.FragmentManagerImpl.dispatchCreateOptionsMenu(FragmentManager.java:1989)
at android.support.v4.app.FragmentActivity.onCreatePanelMenu(FragmentActivity.java:276)
at android.support.v7.app.ActionBarActivity.superOnCreatePanelMenu(ActionBarActivity.java:276)
at android.support.v7.app.ActionBarActivityDelegate$1.onCreatePanelMenu(ActionBarActivityDelegate.java:79)
at android.support.v7.widget.WindowCallbackWrapper.onCreatePanelMenu(WindowCallbackWrapper.java:49)
at android.support.v7.internal.app.ToolbarActionBar.populateOptionsMenu(ToolbarActionBar.java:459)
at android.support.v7.internal.app.ToolbarActionBar$1.run(ToolbarActionBar.java:69)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Change-Id: I5b069c734687ad2622f38eb1510212eedde8bfb5
(cherry picked from commit 75ca999168f6608fc136e80ad5ef98468fa7c414)