fix: Let getFileAttributeView() return null for unsupported view class.

[chbriem]

Issue #, if available:
No issue created this time. If needed, I can create one later.

Description of changes:
Observed when trying to use JDK's Files.move() method. This method uses the java.nio.file.CopyMoveHelper#copyToForeignTarget method. The implementation tries to get the PosixFileAttributeView (in line 109). This fails for the S3 implementation with an UnsupportedOperationException, which is not caught by JDK's code, resulting in the move operation to fail.

Having read the method description, I'm of the opinion that the method should return null in case of an unsupported view type. This would at least be compliant with the method comment in the copyToForeignTarget method (line 108):

// retrieve source posix view, null if unsupported

I've adapted the test accordingly.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[markjschreiber]

Looks good. Thanks!