Fix NPE in DocumentsUI when rotate UI before format as internal

When the device is rotated, the action bar may not have already been
installed (because such installation is done in onCreateOptionsMenu).
Protect against this case.

1.Settings->Storage and USB->SD Card Settings->turn the handset to landscape mode->Format as internal storage.
2.Move data to new storage->Tap Move later

01-03 14:06:34.156  7709  7709 E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.android.documentsui.DocumentsToolBar.hasExpandedActionView()' on a null object reference
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at com.android.documentsui.BaseActivity$SearchManager.cancelSearch(BaseActivity.java:758)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at com.android.documentsui.DocumentsActivity.onBackPressed(DocumentsActivity.java:518)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at com.android.documentsui.DirectoryFragment$4$1.run(DirectoryFragment.java:315)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at android.os.Handler.handleCallback(Handler.java:739)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at android.os.Handler.dispatchMessage(Handler.java:95)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at android.os.Looper.loop(Looper.java:148)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at android.app.ActivityThread.main(ActivityThread.java:5461)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at java.lang.reflect.Method.invoke(Native Method)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
01-03 14:06:34.156  7709  7709 E AndroidRuntime: 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

FEIJ-1160
Change-Id: I7269ff5b9c189fd1fa4d0716b2d4cbc837349dc5
(cherry picked from commit e843aafd)