RFR: 8295456: (ch) sun.nio.ch.Util::checkBufferPositionAligned gives misleading/incorrect error

[Brian Burkhalter]

Improve `IOException` message in `sun.nio.ch.Util::checkBufferPositionAligned`.

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Commit messages:
 - 8295456: (ch) sun.nio.ch.Util::checkBufferPositionAligned gives misleading/incorrect error

Changes: https://git.openjdk.org/jdk/pull/10753/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10753&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295456
  Stats: 10 lines in 1 file changed: 1 ins; 3 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/10753.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10753/head:pull/10753

PR: https://git.openjdk.org/jdk/pull/10753