fix behaviour of parse errors

src/lake.c

@@ -75,6 +75,8 @@ static LakeVal *prompt_read(Env *env, char *prompt)
     /* try to parse a naked call without parens
        (makes the repl more palatable) */
     LakeList *list = parse_naked_list(buf, strlen(buf));
+    if (!list) return NULL;
+
     LakeVal *result;
     
     /* naked call */

src/parse.c

@@ -82,8 +82,8 @@ LakeList *parse_naked_list(char *s, size_t n)
         LakeVal *val = _parse_expr(&ctx);
         if (val == VAL(PARSE_ERR)) {
             list_free(list);
-            list = NULL;
             ctx.i = ctx.n;
+            return NULL;
         }
         list_append(list, val);
     }