RFR: 8377167: javax/imageio/ReadAbortTest.java throw NPE when x11 unavailable

[SendaoYan]

Hi all,

Test javax/imageio/ReadAbortTest.java and javax/imageio/WriteAbortTest.java throw java.lang.NullPointerException when x11 display unavailable, because object `path` unable to initial. This PR check the `path` is null or not before use it, this will make test failure report friendly when x11 display unavailable but DISPLAY was seted.

Change has been verified locally on linux-x64.

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Commit messages:
 - 8377167: javax/imageio/ReadAbortTest.java throw NPE when x11 unavailable

Changes: https://git.openjdk.org/jdk/pull/29569/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29569&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377167
  Stats: 23 lines in 2 files changed: 13 ins; 7 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/29569.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29569/head:pull/29569

PR: https://git.openjdk.org/jdk/pull/29569