Fix file leak when using metadata functions

[pablobaxter]

Discovered this issue via the wire project.

The issue here is that the ZipFileSystem creates a Source object, which is then returned out of the use lambda, which the lambda is supposed to close the FileHandle that is created, however, because the Source object had not been closed, the FileHandle remains open.

val source = fileSystem.openReadOnly(zipPath).use { fileHandle ->
  fileHandle.source(entry.offset).buffer()
}
return source.readLocalHeader(basicMetadata)

Going into a bit more detail, the openStreamCount is not 0 because the Source object wasn't closed, so we never close the underlying RandomAccessFile that was opened.

@Throws(IOException::class)
final override fun close() {
  lock.withLock {
    if (closed) return
    closed = true
    if (openStreamCount != 0) return
  }
  protectedClose()
}

This fix ensures the Source object is closed once the metadata has been extracted. This issue also occurs when calling exists() in the ZipFileSystem.

Closes #1356

[JakeWharton]

#1356 has a test. Can we copy that in so as to not regress?

[swankjesse]

Much better

[swankjesse]

Thanks for finding this and also for fixing this. Your test is brilliant too. Yay!