RFR: 8277087: ZipException: zip END header not found at ZipFile#Source.findEND

[Sergey Bylokhov]

The ZipOutputStream class may create bogus zip data which cannot be opened by the ZipFile. The root cause is how the comment field is stored by the ZipOutputStream. According to the zip specification, the comment field should not be longer than 0xFFFF bytes, and we try to validate the length of the comment, but unfortunately, we do this after the comment was assigned already. So if the application saves the comment based on the user's input and then gets an exception from the ZipOutputStream.setComment() it may assume that the comment is too long and it will be ignored, but it will be saved as-is to the file.

Please take a look at [this](https://github.com/openjdk/jdk/commit/c435a0905dfae827687ed46015269f9c1b36c239#diff-736e247f0ec294323891a77e16a9f0dba8bc1872131c857edf18c3f349e750eeL117) refactoring, and note:
 * The comment field is assigned before the length check
 * The null comment is ignored

The current fix will move the length validation before being assigned and will use the null comment as an empty text. Note that the behavior of the null parameter is not specified in the method/class/package so we are free here to implement it in any way, any thoughts/suggestions on which is better?

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Commit messages:
 - Initial version JDK-8277087

Changes: https://git.openjdk.java.net/jdk/pull/6380/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6380&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277087
  Stats: 101 lines in 2 files changed: 98 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6380.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6380/head:pull/6380

PR: https://git.openjdk.java.net/jdk/pull/6380