dpkg-deb: work around bogus error message when working with XZ compressed packages

function                                             old     new   delta
unpack_xz_stream                                    2309    2317      +8
bb_full_fd_action                                    464     472      +8

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/archival/libarchive/unxz/xz_stream.h b/archival/libarchive/unxz/xz_stream.h
index 66cb5a7..45056e4 100644
--- a/archival/libarchive/unxz/xz_stream.h
+++ b/archival/libarchive/unxz/xz_stream.h
@@ -25,7 +25,7 @@
 
 #define STREAM_HEADER_SIZE 12
 
-#define HEADER_MAGIC "\3757zXZ"
+#define HEADER_MAGIC "\375""7zXZ"
 #define HEADER_MAGIC_SIZE 6
 
 #define FOOTER_MAGIC "YZ"