RFR: 8304685: heap-buffer-overflow in libjdwp

[Kevin Walls]

Problem call to skipWhitespace in dbgsysExec src/jdk.jdwp.agent/unix/native/libjdwp/exec_md.c:91

We call skipWhitespace even when the loop will terminate, should guard against the last skipWhitespace call on the last iteration.

Could be done differently with the skipWhitespace call at the start of the loop, but skipped on the first iteration, but leaving the statements in the loop in the same order seems more readable.

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Commit messages:
 - comment tweak
 - 8304685: heap-buffer-overflow in libjdwp

Changes: https://git.openjdk.org/jdk/pull/13964/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13964&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304685
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13964.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13964/head:pull/13964

PR: https://git.openjdk.org/jdk/pull/13964