contrib: ccan/json possible uninitialized use

contrib/ccan/json/json.c

@@ -793,7 +793,7 @@ failure:
 bool parse_string(const char **sp, char **out)
 {
 	const char *s = *sp;
-	SB sb;
+	SB sb = { NULL, NULL, NULL };
 	char throwaway_buffer[4];
 		/* enough space for a UTF-8 character */
 	char *b;