NSData: fix an errno stomp

We would attempt to remove the temporary file.  However, that will
result in calls which can destroy the original errno.  Save the previous
errno before performing the cleanup.

Author: compnerd

Foundation/NSData.swift

@@ -517,8 +517,9 @@ open class NSData : NSObject, NSCopying, NSMutableCopying, NSSecureCoding {
             if let auxFilePath = auxFilePath {
                 try fm._fileSystemRepresentation(withPath: auxFilePath, { auxFilePathFsRep in
                     if rename(auxFilePathFsRep, pathFsRep) != 0 {
+                        let savedErrno = errno
                         try? FileManager.default.removeItem(atPath: auxFilePath)
-                        throw _NSErrorWithErrno(errno, reading: false, path: path)
+                        throw _NSErrorWithErrno(savedErrno, reading: false, path: path)
                     }
                     if let mode = mode {
                         chmod(pathFsRep, mode)