RFR: 8266078: Reader.read(CharBuffer) advances Reader position for read-only Charbuffers [v2]

[Brian Burkhalter]

> Please consider this request to modify `Reader.read(CharBuffer)` to check whether the buffer is read-only before reading any characters from the character stream. This can happen now if the buffer is read-only. Character are first read thereby advancing the stream before an attempt is made to put them in the `CharBuffer` thus incorrectly advancing the stream position.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8266078: Make read-only check global; add message in test

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3725/files
  - new: https://git.openjdk.java.net/jdk/pull/3725/files/2fbaff7d..4a899b26

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3725&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3725&range=00-01

  Stats: 8 lines in 2 files changed: 5 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3725.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3725/head:pull/3725

PR: https://git.openjdk.java.net/jdk/pull/3725