wwdump: fail ast mode on parser errors

selfhost/cmd/wwdump/main.ww

@@ -114,6 +114,7 @@ export fn main(argc: i32, argv: **u8) i32 = {
 		parserinit(&ps, &l);
 		let f: *node = parsefile(&ps);
 		astprint(1i32, f);
+		if (ps.errs > 0) { return 1; };
 	} else { if (mode == 114) {	// '-r' — name resolve report
 		let ps: parser;
 		parserinit(&ps, &l);