Fix off-by-one error for declarative marking

The for loops for marking and reference updating declaratively marked
TypedData objects did not mark/reference update the very last element.

When RGENGC_CHECK_MODE is turned on, this caused the test in Enumerator
to fail with:

    tool/lib/test/unit/testcase.rb:173:in `rescue in run': failed to allocate memory (NoMemoryError)

gc.c

@@ -7444,7 +7444,7 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
                 if (RTYPEDDATA_P(obj) && gc_declarative_marking_p(any->as.typeddata.type)) {
                     size_t *offset_list = (size_t *)RANY(obj)->as.typeddata.type->function.dmark;
 
-                    for (size_t offset = *offset_list; *offset_list != RUBY_REF_END; offset = *offset_list++) {
+                    for (size_t offset = *offset_list; offset != RUBY_REF_END; offset = *offset_list++) {
                         rb_gc_mark_movable(*(VALUE *)((char *)ptr + offset));
                     }
                 }
@@ -10814,7 +10814,7 @@ gc_update_object_references(rb_objspace_t *objspace, VALUE obj)
                 if (RTYPEDDATA_P(obj) && gc_declarative_marking_p(any->as.typeddata.type)) {
                     size_t *offset_list = (size_t *)RANY(obj)->as.typeddata.type->function.dmark;
 
-                    for (size_t offset = *offset_list; *offset_list != RUBY_REF_END; offset = *offset_list++) {
+                    for (size_t offset = *offset_list; offset != RUBY_REF_END; offset = *offset_list++) {
                         VALUE *ref = (VALUE *)((char *)ptr + offset);
                         if (SPECIAL_CONST_P(*ref)) continue;
                         *ref = rb_gc_location(*ref);

test/ruby/test_enumerator.rb

@@ -862,6 +862,20 @@ def test_lazy_chain
     assert_equal(33, chain.next)
   end
 
+  def test_lazy_chain_under_gc_compact_stress
+    EnvUtil.under_gc_compact_stress do
+      ea = (10..).lazy.select(&:even?).take(10)
+      ed = (20..).lazy.select(&:odd?)
+      chain = (ea + ed).select{|x| x % 3 == 0}
+      assert_equal(12, chain.next)
+      assert_equal(18, chain.next)
+      assert_equal(24, chain.next)
+      assert_equal(21, chain.next)
+      assert_equal(27, chain.next)
+      assert_equal(33, chain.next)
+    end
+  end
+
   def test_chain_undef_methods
     chain = [1].to_enum + [2].to_enum
     meths = (chain.methods & [:feed, :next, :next_values, :peek, :peek_values])