RFR: 8352420: [ubsan] codeBuffer.cpp:984:27: runtime error: applying non-zero offset 18446744073709486080 to null pointer [v2]

[Doug Simon]

> This PR addresses undefined behavior in CodeBuffer by making `verify_section_allocation` return early for a partially initialized CodeBuffer.

Doug Simon has updated the pull request incrementally with two additional commits since the last revision:

 - initialize _total_start with nullptr instead of 0
 - moved initialization of _total_start and _total_size

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24118/files
  - new: https://git.openjdk.org/jdk/pull/24118/files/bbab41b7..15d90178

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24118&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24118&range=00-01

  Stats: 5 lines in 2 files changed: 2 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24118.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24118/head:pull/24118

PR: https://git.openjdk.org/jdk/pull/24118