Fix crash when showing inspect menu of invalid provider

Files app crashes when opening the inspect menu of invalid document
provider. This CL disables the inspect menu when the DocumentInfo of
current directory is null.

Bug: 79128117
Test: Added new coverage.
Test: Run instrumentation tests from com.android.documentsui.tests
Change-Id: I4de296fb976b7e54bbd3bce98d14192ca5c25e1a
2 files changed