AAPT2: binary parser should be more lenient with files

Some APKs have file references that reference files that don't exist.

For now, just be lenient and ignore the files themselves.

Keep the actual reference until such a time as general resource
stripping is implemented.

Bug: 37749644
Test: manual
Change-Id: I773685acf41212405b71b064d64045fb4556dcfc