zcat: complain if input is not compressed

function                                             old     new   delta
buffer_fill_and_print                                178     191     +13
varvalue                                             735     743      +8
bbunpack                                             747     755      +8
open_zipped                                           85      89      +4
xmalloc_open_zipped_read_close                        61      63      +2
get_addr_1                                           240     242      +2
fbsplash_main                                       1228    1230      +2
pstree_main                                          322     321      -1
builtin_type                                         121     119      -2
do_load                                              954     926     -28
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 7/3 up/down: 39/-31)              Total: 8 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/archival/libarchive/get_header_tar.c b/archival/libarchive/get_header_tar.c
index 54d9104..ba43bb0 100644
--- a/archival/libarchive/get_header_tar.c
+++ b/archival/libarchive/get_header_tar.c
@@ -243,7 +243,7 @@
 		 * or not first block (false positive, it's not .gz/.bz2!) */
 		if (lseek(archive_handle->src_fd, -i, SEEK_CUR) != 0)
 			goto err;
-		if (setup_unzip_on_fd(archive_handle->src_fd, /*fail_if_not_detected:*/ 0) != 0)
+		if (setup_unzip_on_fd(archive_handle->src_fd, /*fail_if_not_compressed:*/ 0) != 0)
  err:
 			bb_error_msg_and_die("invalid tar magic");
 		archive_handle->offset = 0;