RFR: 8335536: Fix assertion failure in IdealGraphPrinter when append is true

[Qizheng Xing]

When `IdealGraphPrinter` is created with `append` set to true, it does not write the head element to the file in its constructor. But in the destructor, it always writes the tail element to the file no matter `append` is true or not, which causes an assertion failure in `xmlStream::pop_tag`.

This issue can be reproduced by calling `igv_append` directly, or by calling `Compile::igv_print_method_to_file` with `append` set to true.

This patch fixes the issue.

-------------

Commit messages:
 - Fix assertion fail in `IdealGraphPrinter` when `append` is true.

Changes: https://git.openjdk.org/jdk/pull/19986/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19986&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335536
  Stats: 18 lines in 2 files changed: 7 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/19986.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19986/head:pull/19986

PR: https://git.openjdk.org/jdk/pull/19986