Download to tmp file handling

UrlSessionDelegate.m

-(void)URLSession:(NSURLSession *)session
      downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
    NSParameterAssert( nil != location );
    
    if ( self->_shouldCopyTmpFileToCaches )
    {
        JFFAsyncOperation asyncCopy = [ [ self class ] asyncCopyFileToCaches: location ];
        asyncCopy( nil, nil, ^void( NSURL* tmpFileInCaches, NSError* copyError )
        {
            [ self onSuccessfulDownloadToTmpFile: tmpFileInCaches
                                   copyFileError: copyError ];
        } );
    }
    else
    {
        [ self onSuccessfulDownloadToTmpFile: location
                               copyFileError: nil ];
    }
}