[jdk21u-dev] RFR: 8335536: Fix assertion failure in IdealGraphPrinter when append is true

[Qizheng Xing]

Hi all,

This pull request contains a backport of commit [6db4c6a7](https://github.com/openjdk/jdk/commit/6db4c6a772df856fc3099c32a5b2c102a30d360c) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.

The commit being backported was authored by Qizheng Xing on 3 Jul 2024 and was reviewed by Tobias Hartmann, Christian Hagedorn and Tobias Holenstein.

Thanks!

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Commit messages:
 - Backport 6db4c6a772df856fc3099c32a5b2c102a30d360c

Changes: https://git.openjdk.org/jdk21u-dev/pull/816/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=816&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335536
  Stats: 22 lines in 2 files changed: 11 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/816.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/816/head:pull/816

PR: https://git.openjdk.org/jdk21u-dev/pull/816