409953 return buffer.slice() instead of buffer.asReadOnlyBuffer() in ResourceCache to avoid using inefficent path in BufferUtil.writeTo

jetty-server/src/main/java/org/eclipse/jetty/server/ResourceCache.java

@@ -486,7 +486,7 @@ public class ResourceCache
             }
             if (buffer==null)
                 return null;
-            return buffer.asReadOnlyBuffer();
+            return buffer.slice();
         }