RFR: 8297211: Expensive fillInStackTrace operation in HttpURLConnection.getOutputStream0 when no content-lenght in response

[Jaikiran Pai]

Can I please get a review for this small change which addresses https://bugs.openjdk.org/browse/JDK-8297211? 
The change checks if the `content-length` header value is present before parsing it into a `Long` value. The commit also now catches the more specific `NumberFormatException` instead of a general `Exception`. Given the context of the code, I believe this change in the exception type in the catch block should be fine.

No new test has been introduced given the nature of this change. I have triggered existing tests to verify no unexpected regressions show up.

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Commit messages:
 - 8297211: Expensive fillInStackTrace operation in HttpURLConnection.getOutputStream0 when no content-lenght in response

Changes: https://git.openjdk.org/jdk/pull/11258/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11258&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297211
  Stats: 8 lines in 1 file changed: 5 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11258.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11258/head:pull/11258

PR: https://git.openjdk.org/jdk/pull/11258