RFR: 8267833: Improve G1CardSetInlinePtr::add()

[Ivan Walulya]

Hi all,

Please review this cleanup change to reduce the number of comparisons made when adding entries to an inline pointer cardset container. We allow the find to restart from a previously known index.

Testing: Tier 1-3

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Commit messages:
 - cleanup
 - change location of the assert
 - chaange asseert to if check
 - 8267833: Improve G1CardSetInlinePtr::add()

Changes: https://git.openjdk.java.net/jdk/pull/5067/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5067&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267833
  Stats: 25 lines in 2 files changed: 18 ins; 1 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5067.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5067/head:pull/5067

PR: https://git.openjdk.java.net/jdk/pull/5067