Refine testConfig_trustedQuickViewerPackage_isNotEmpty

Root Cause : Some projects like x86 emulator or AOSP
do not integrate overlay package for trusted_quick_viewer_package,
and AOSP do not define content for default value
that will cause testCase assert fail in some cases(flaky)

Fix:128838041
Test: atest DocumentsUITests
      atest DocumentsUIGoogleTests

Change-Id: I55da53e589c7fcc195308686287e5fe72c11ef1d