Check Local<UnboundModuleScript> before producing cache

ProduceCacheInternal()'s |unbount_script| argument can be
empty for module scripts and this is causing crash.

Bug: 938269, 841466
Change-Id: I2e51702fa243c9e1486511ddbe7e845c2b5b4a34
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1507112
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638747}

third_party/blink/renderer/bindings/core/v8/v8_code_cache.cc

@@ -213,6 +213,10 @@ static void ProduceCacheInternal(
       V8CodeCache::SetCacheTimeStamp(cache_handler);
       break;
     case V8CodeCache::ProduceCacheOptions::kProduceCodeCache: {
+      // TODO(crbug.com/938269): Investigate why this can be empty here.
+      if (unbound_script.IsEmpty())
+        break;
+
       constexpr const char* kTraceEventCategoryGroup = "v8,devtools.timeline";
       TRACE_EVENT_BEGIN1(kTraceEventCategoryGroup, trace_name, "fileName",
                          source_url.GetString().Utf8());