added lox test files

lox.t/closure/close_over_later_variable.lox

@@ -0,0 +1,15 @@
+// This is a regression test. There was a bug where if an upvalue for an
+// earlier local (here "a") was captured *after* a later one ("b"), then it
+// would crash because it walked to the end of the upvalue list (correct), but
+// then didn't handle not finding the variable.
+
+fun f() {
+  var a = "a";
+  var b = "b";
+  fun g() {
+    print b; // expect: b
+    print a; // expect: a
+  }
+  g();
+}
+f();