mojo: Fix Java binding generator for array<enum>

Values should be validated by iterating with i{{level+1}}.

BUG=1148220

Change-Id: Iaa837dd73091c0f938bb2461569f3b46d04920b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532547Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Commit-Queue: Ryo Hashimoto <hashimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827115}

mojo/public/tools/bindings/generators/java_templates/data_types_definition.tmpl

@@ -100,8 +100,8 @@ if ({{variable}} != null) {
 {%-     else %}
 {
 {%-     endif %}
-    for (int i{{level}} = 0; i{{level}} < {{variable}}.length; ++i{{level}}) {
-        {{kind.kind|java_class_for_enum}}.validate({{variable}}[i{{level}}]);
+    for (int i{{level+1}} = 0; i{{level+1}} < {{variable}}.length; ++i{{level+1}}) {
+        {{kind.kind|java_class_for_enum}}.validate({{variable}}[i{{level+1}}]);
     }
 }
 {%-   elif kind|is_enum_kind %}