idmap2: ZipFile::Open: fix potential memory leak

Even if OpenArchive in libziparchive returns a non-zero value
(indicating failure), it will have allocated memory that needs to be
freed via CloseArchive. Add the missing call.

Test: valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1 $ANDROID_HOST_OUT/nativetest64/idmap2_tests/idmap2_tests
Change-Id: I92d47459c27e62ba4544327d7b7f3c4106e6ad34