Issue #362 (Very slow page load and missing resources when using HTTP/2 with Jetty 9.3.7)

The issue happened when the selector was both read ready and write
ready. In that case fillable() was called before completeWrite(),
causing the reader thread to read, parse, call the application which
performed a blocking write, thus never returning to call
completeWrite().

Inverting the calls (first completeWrite() then fillable()) solves
the issue because completeWrite() never calls application code.

jetty-io/src/main/java/org/eclipse/jetty/io/SelectChannelEndPoint.java

@@ -118,8 +118,8 @@ public class SelectChannelEndPoint extends ChannelEndPoint implements ManagedSel
         @Override
         public void run()
         {
-            getFillInterest().fillable();
             getWriteFlusher().completeWrite();
+            getFillInterest().fillable();
         }
 
         @Override