Add test for #6376

tests/unit/src/unit/issues/Issue6376.hx

@@ -0,0 +1,9 @@
+package unit.issues;
+
+class Issue6376 extends Test {
+	public function test() {
+		var s:Dynamic = "foo";
+		var indexOf = Reflect.field(s, "indexOf");
+		eq(Reflect.callMethod(s, indexOf, ["o", 0]), 1);
+	}
+}