tar: compat: handle tarballs with only one zero block at the end

diff --git a/archival/libunarchive/get_header_tar.c b/archival/libunarchive/get_header_tar.c
index 274bd46..7493d91 100644
--- a/archival/libunarchive/get_header_tar.c
+++ b/archival/libunarchive/get_header_tar.c
@@ -90,7 +90,15 @@
 
  again_after_align:
 
-	xread(archive_handle->src_fd, &tar, 512);
+	i = full_read(archive_handle->src_fd, &tar, 512);
+	/* if GNU tar sees EOF in above read, it says:
+	 * "tar: A lone zero block at N", where N = kilobyte
+	 * where EOF was met (not EOF block, actual EOF!),
+	 * and tar will exit with error code 0! Mimic exit(0): */
+	if (i == 0)
+		xfunc_error_retval = 0;
+	if (i != 512)
+		bb_error_msg_and_die("short read");
 	archive_handle->offset += 512;
 
 	/* If there is no filename its an empty header */