Merge r407 from trunk, in order to fix
Issue 3: http://code.google.com/p/libarchive/issues/detail?id=3

SVN-Revision: 408
diff --git a/libarchive/archive_write_disk.c b/libarchive/archive_write_disk.c
index ef10723..844a294 100644
--- a/libarchive/archive_write_disk.c
+++ b/libarchive/archive_write_disk.c
@@ -519,6 +519,9 @@
 	ssize_t bytes_written = 0;
 	ssize_t block_size = 0, bytes_to_write;
 
+	if (size == 0)
+		return (ARCHIVE_OK);
+
 	if (a->filesize == 0 || a->fd < 0) {
 		archive_set_error(&a->archive, 0,
 		    "Attempt to write to an empty file");