RFR: 8248908: Printer.createPageLayout() returns 0.75"margins instead of hardware margins

[Phil Race]

For a Media that had no defined size - eg a "custom" paper - the code was creating a mapping
that over-rode the NA_LETTER size. This might cause multiple problems but definitely meant that
we ended up with default margins.

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Commit messages:
 - 8248908: Printer.createPageLayout() returns 0.75"margins instead of hardware margins

Changes: https://git.openjdk.java.net/jfx/pull/266/files
 Webrev: https://webrevs.openjdk.java.net/jfx/266/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248908
  Stats: 129 lines in 2 files changed: 117 ins; 8 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/266.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/266/head:pull/266

PR: https://git.openjdk.java.net/jfx/pull/266