RFR: 8364146: JList getScrollableUnitIncrement return 0 [v6]

[Prasanta Sadhukhan]

> It seems JList.getScrollableUnitIncrement can sometime return 0 instead of positive number which is not specified in the javadoc which can lead to confusion. Clarified javadoc as to when it can return 0.

Prasanta Sadhukhan has updated the pull request incrementally with two additional commits since the last revision:

 - Review comment fix
 - Review comment fix

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26500/files
  - new: https://git.openjdk.org/jdk/pull/26500/files/5e2e413e..9224a1a8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26500&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26500&range=04-05

  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26500.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26500/head:pull/26500

PR: https://git.openjdk.org/jdk/pull/26500