RFR: 8301964: Expensive fillInStackTrace operation in HttpURLConnection.getLastModified when no last-modified in response [v3]

[Andrey Turbanov]

> [JDK-8297211](https://bugs.openjdk.org/browse/JDK-8297211) (#11258) missed one case with date headers: `last-modified`, `date`, `expires`. We can avoid expensive NPE.

Andrey Turbanov has updated the pull request incrementally with one additional commit since the last revision:

  8301964: Expensive fillInStackTrace operation in HttpURLConnection.getLastModified when no last-modified in response
  
  update copyright year

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12451/files
  - new: https://git.openjdk.org/jdk/pull/12451/files/b836a2c3..e2690ee1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12451&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12451&range=01-02

  Stats: 4 lines in 2 files changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12451.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12451/head:pull/12451

PR: https://git.openjdk.org/jdk/pull/12451