RFR: 6355567: AdobeMarkerSegment causes failure to read valid JPEG

[Liam Miller-Cushon]

Please review this fix for JDK-6355567, which updates AdobeMarkerSegment to use the reported length of the segment instead of assuming it's always exactly 14 bytes.

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Commit messages:
 - 6355567: AdobeMarkerSegment causes failure to read valid JPEG

Changes: https://git.openjdk.org/jdk/pull/14779/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14779&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-6355567
  Stats: 69 lines in 3 files changed: 61 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/14779.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14779/head:pull/14779

PR: https://git.openjdk.org/jdk/pull/14779