libandroidfw: Fix mass logspam of ResourceTypes warnings

An overlay was incorrectly leaking its own resources into the
framework resource package, which caused warnings for every app
that tried to access framework resources (all of them).

This change skips including any resources that are not overlaying
anything (not present in IDMAP).

Bug: 36256974
Test: make libandroidfw_tests
Change-Id: I8c710af6849bb848938825aacca02799ee96c003