RFR: 5043343: FileImageInputStream and FileImageOutputStream do not properly track streamPos for RandomAccessFile

[Brian Burkhalter]

In the respective constructors, set the value of the initial stream position to the current file position.

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Commit messages:
 - 5043343: FileImageInputStream and FileImageOutputStream do not properly track streamPos for RandomAccessFile

Changes: https://git.openjdk.org/jdk/pull/24283/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24283&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-5043343
  Stats: 112 lines in 3 files changed: 110 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/24283.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24283/head:pull/24283

PR: https://git.openjdk.org/jdk/pull/24283