rtld.c: avoid double-free on dso load failure in do_load_object()

The obj->path is assigned directly from the path argument, and
load_object() frees the path on do_load_object() failure.  Do not free
it in obj_free() on the error path.

Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D60402

libexec/rtld-elf/rtld.c

@@ -3027,6 +3027,7 @@ do_load_object(int fd, const char *name, char *path, struct stat *sbp,
 
 errp:
 	munmap(obj->mapbase, obj->mapsize);
+	obj->path = NULL;	/* obj->path is owned and freed by caller */
 	obj_free(obj);
 	return (NULL);
 }