Fix NUL byte check for object keys

src/load.c

@@ -699,7 +699,7 @@ static json_t *parse_object(lex_t *lex, size_t flags, json_error_t *error)
         key = lex_steal_string(lex, &len);
         if(!key)
             return NULL;
-        if (memchr(key, len, '\0')) {
+        if (memchr(key, '\0', len)) {
             jsonp_free(key);
             error_set(error, lex, "NUL byte in object key not supported");
             goto error;

test/suites/invalid/null-byte-in-object-key/error

@@ -0,0 +1,2 @@
+1 15 15
+NUL byte in object key not supported near '"foo\u0000bar"'

test/suites/invalid/null-byte-in-object-key/input

@@ -0,0 +1 @@
+{"foo\u0000bar": 42}