RFR: 8283756: [testbug] Only verify inflated bytes in ZipFSOutputStreamTest

[Volker Simonis]

The test `ZipFSOutputStreamTest` deflates content into a zip file system and subsequently inflates the deflated files and checks their content against the original data.

The content consists of a data stream of bytes with the value `42`.

The check currently compares the temporary inflation buffer with the original source buffer, no matter how many bytes were inflated into the inflation buffer. This can lead to problems with alternative zlib implementations which sometimes write beyond the last inflated byte (see [JDK-8282648](https://bugs.openjdk.java.net/browse/JDK-8282648) for more details).

The fix is trivial. Only compare as many bytes as have been inflated against the original content.

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Commit messages:
 - 8283756: [testbug] Only verify inflated bytes in ZipFSOutputStreamTest

Changes: https://git.openjdk.java.net/jdk/pull/7984/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7984&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283756
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7984.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7984/head:pull/7984

PR: https://git.openjdk.java.net/jdk/pull/7984