Bug: http://b/119818070 "app crashes when reading asset of zero length"
Add support for zero-length mappings for the Windows code path as well.
Test: ran libbase_test on Windows under wine.
Change-Id: Iccb65fa800c636444100c9369f41e36d24a53a99
This allows us to remove libziparchive's dependency on libutils.
Bug: http://b/79112958
Test: ran libbase and libziparchive tests, ran fastboot manually
Change-Id: I95c651976dad222863e5b8c37d4514b778f5dce7