Fix HDR sluggish issue.

- skip writing blobs if empty packet is sent for per-frame metadata.

Bug: 274050717
Test: play HDR video on YouTube
Change-Id: If8716613136c70a5adee29074cc2e9d35a500264
diff --git a/graphics/composer/2.3/utils/command-buffer/include/composer-command-buffer/2.3/ComposerCommandBuffer.h b/graphics/composer/2.3/utils/command-buffer/include/composer-command-buffer/2.3/ComposerCommandBuffer.h
index afc22d8..5e9a287 100644
--- a/graphics/composer/2.3/utils/command-buffer/include/composer-command-buffer/2.3/ComposerCommandBuffer.h
+++ b/graphics/composer/2.3/utils/command-buffer/include/composer-command-buffer/2.3/ComposerCommandBuffer.h
@@ -87,6 +87,10 @@
             return;
         }
 
+        if (metadata.size() == 0) {
+            return;
+        }
+
         // space for numElements
         commandLength += 1;