RFR: 8251242: Tile based rendering results in artifacts in last column while using metal pipeline

[Ajit Ghaisas]

Issue : https://bugs.openjdk.java.net/browse/JDK-8251242
Fix : Corrected offsets in case of partial image area copy. Also removed incorrect debug statement.

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Commit messages:
 - 8251242_image_copy_fix

Changes: https://git.openjdk.java.net/lanai/pull/76/files
 Webrev: https://webrevs.openjdk.java.net/lanai/76/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251242
  Stats: 25 lines in 1 file changed: 15 ins; 9 del; 1 mod
  Patch: https://git.openjdk.java.net/lanai/pull/76.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/76/head:pull/76

PR: https://git.openjdk.java.net/lanai/pull/76