Fix logic bug in ReplMgr when no assets are present

Commit 72e0ca15 added a callback to handle loading of assets to the
Companion. However, if the Companion is connected to a project without
assets, the callback to switch from ASSET state to CONNECTED state
will never fire. This commit checks whether the asset map has 0
elements, in which case it will synchronously fire the callback so
that projects without assets will immediately transition to CONNECTED
state.

Change-Id: Iba12232966752ed9cb61af0f97aa16ebcffeed4a

appinventor/appengine/src/com/google/appinventor/client/AssetManager.java

@@ -210,6 +210,10 @@ public final class AssetManager implements ProjectChangeListener {
         }
       }
     }
+    // If no assets are in the project, perform the callback immediately.
+    if (assets.values().size() == 0 && assetsTransferredCallback != null) {
+      doCallBack(assetsTransferredCallback);
+    }
   }
 
   public static void refreshAssets(String formName, JavaScriptObject callback) {