RFR: 8283332: G1: Stricter assertion in G1BlockOffsetTablePart::forward_to_block_containing_addr

[Albert Mingkun Yang]

Stricter assertion to match the assert message.

Test: hotspot_gc

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Commit messages:
 - g1-bot

Changes: https://git.openjdk.java.net/jdk/pull/7856/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7856&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283332
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7856.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7856/head:pull/7856

PR: https://git.openjdk.java.net/jdk/pull/7856