Fix crash when opening inspector screen of broken folder

Files app crashes when opening inspector screen of the invalid folder,
such as top folder of the document root doesn't exist.

This CL disable the inspector menu of such invalid folder by checking
the query result of current directly.

Bug: 112321403
Test: Manual
Test: Run instrumentation tests from com.android.documentsui.tests
Change-Id: I6ebce6970bdf62707ceb359e81d5bd5f889184e4