Fix a warning and potential segfault in lash when BB_FEATURE_CLEAN_UP
is enabled
diff --git a/lash.c b/lash.c
index 0af6691..22e3c77 100644
--- a/lash.c
+++ b/lash.c
@@ -1507,8 +1507,8 @@
 #ifdef BB_FEATURE_CLEAN_UP
 void free_memory(void)
 {
-	if (cwd) {
-		free(cwd);
+	if (cwd && cwd!=unknown) {
+		free((char*)cwd);
 	}
 	if (local_pending_command)
 		free(local_pending_command);