This patch was fed back to the upstream community:
http://code.google.com/p/libarchive/issues/detail?id=288
Given the response "This issue has been already fixed in master branch."
it should no longer be needed with the next release.

--- libarchive/libarchive/archive_string.c.orig	Mon Mar 26 19:49:00 2012
+++ libarchive/libarchive/archive_string.c	Tue Nov 27 18:10:35 2012
@@ -1120,8 +1120,8 @@
 	}
 	sc->to_charset = strdup(tc);
 	if (sc->to_charset == NULL) {
-		free(sc);
 		free(sc->from_charset);
+		free(sc);
 		return (NULL);
 	}
 	archive_string_init(&sc->utftmp);