[code-reflection] RFR: More block checks

[Paul Sandoz]

More robust checking for empty blocks or non-empty blocks with no terminating operation.

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Commit messages:
 - More block checks

Changes: https://git.openjdk.org/babylon/pull/15/files
 Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=15&range=00
  Stats: 74 lines in 2 files changed: 51 ins; 6 del; 17 mod
  Patch: https://git.openjdk.org/babylon/pull/15.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/15/head:pull/15

PR: https://git.openjdk.org/babylon/pull/15