RFR: 8368097: [asan] heap-buffer-overflow reported in ClassFileParser::skip_over_field_signature

[Johan Sjölen]

Hi,

`skip_over_field_name` may produce a pointer which is exactly one `char` of bounds, which is the dereferenced by `skip_over_field_signature` when it looks for a semi-colon. This causes an out-of-bounds read, which ASAN caught. The fix is to check whether it's OK to dereference `p` or not.

We keep the semantics the same other than that, so `skip_over_field_signature` and `skip_over_field_name` can both return a pointer which is one past the valid memory range. Creating such a pointer is explicitly not UB, but dereferencing it is.

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Commit messages:
 - Gotta cast
 - Change, add assertion
 - Fix
 - Check whether the next character is in bounds

Changes: https://git.openjdk.org/jdk/pull/27528/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27528&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368097
  Stats: 7 lines in 1 file changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27528.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27528/head:pull/27528

PR: https://git.openjdk.org/jdk/pull/27528