Fix support for @empty in style resolution

If @empty is encountered in XML, do not fallback
to searching through the theme.

Bug: 36891052
Test: make aapt2_tests
Test: bit CtsContentTestCases:android.content.res.cts.TypedArrayTest
Change-Id: Ie3bf7b70af9c7913513a1092afd95d26bec5e635