Allow exploded module readers created for exploded system images to support preview mode.
------------- Commit messages: - Preview mode for exploded system module readers Changes: https://git.openjdk.org/valhalla/pull/2032/files Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2032&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8377162 Stats: 150 lines in 4 files changed: 135 ins; 1 del; 14 mod Patch: https://git.openjdk.org/valhalla/pull/2032.diff Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2032/head:pull/2032 PR: https://git.openjdk.org/valhalla/pull/2032
