RFR: 8229899: java.io.File.isInvalid() is racy

[Arthur Eubanks]

Bug: https://bugs.openjdk.java.net/browse/JDK-8229899
Webrev: http://cr.openjdk.java.net/~aeubanks/8229899/webrev.00/

    final boolean isInvalid() {
        if (status == null) {
            status = (this.path.indexOf('\u0000') < 0) ? PathStatus.CHECKED
                                                       :
PathStatus.INVALID;
        }
        return status == PathStatus.INVALID;
    }
If the reads to "status" are reordered and another thread writes to
"status", the return value can be wrong.
Reading "status" to a local variable fixes the issue.