Add error log

Co-authored-by: David Brochart <david.brochart@gmail.com>

Author: martinRenou

src/notebookrenderer/yCommProvider.ts

@@ -185,7 +185,7 @@ namespace Private {
         break;
       }
       default:
-        break;
+        console.error('Unable to compute message');
     }
     return encoder;
   }