add test (closes #4729)

tests/unit/src/unit/issues/Issue4729.hx

@@ -0,0 +1,18 @@
+package unit.issues;
+
+class Issue4729 extends Test {
+	function test() {
+		var raw = "Hello world !!!";
+
+		var cursor:Int = 0;
+		inline function adv(char:String = " ", ?start:Int) {
+			cursor = raw.indexOf(char, start);
+			return cursor = (cursor > -1 ? cursor : raw.length) + char.length;
+		}
+
+		var hello = raw.substring(0, adv());
+		var world = raw.substring(cursor, adv(cursor));
+		eq("Hello ", hello);
+		eq("world ", world);
+	}
+}