RFR: 8371645: BasicImageReader getEntryNames() is stateful and cannot be called more than once

[David Beaumont]

Stop entry name creation using a stateful read of underlying buffer (which moves the position and consumes it).

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Commit messages:
 - Make entry name reading idempotent

Changes: https://git.openjdk.org/jdk/pull/28263/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28263&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371645
  Stats: 7 lines in 1 file changed: 0 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/28263.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28263/head:pull/28263

PR: https://git.openjdk.org/jdk/pull/28263