Fix memory leak in DefaultChannelHandlerContext

.. where freeInbound() and freeOutbound() are not called for all contexts

- Fixes #1298

transport/src/main/java/io/netty/channel/DefaultChannelHandlerContext.java

@@ -1467,16 +1467,15 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
 
     private void invokeFreeInboundBuffer0() {
         ChannelHandler handler = handler();
-        if (handler instanceof ChannelInboundHandler) {
-            ChannelInboundHandler h = (ChannelInboundHandler) handler;
         try {
-                h.freeInboundBuffer(this);
+            if (handler instanceof ChannelInboundHandler) {
+                ((ChannelInboundHandler) handler).freeInboundBuffer(this);
+            }
         } catch (Throwable t) {
             notifyHandlerException(t);
         } finally {
             freeInbound();
         }
-        }
 
         if (next != null) {
             DefaultChannelHandlerContext nextCtx = findContextInbound();
@@ -1519,16 +1518,15 @@ final class DefaultChannelHandlerContext extends DefaultAttributeMap implements
 
     private void invokeFreeOutboundBuffer0() {
         ChannelHandler handler = handler();
-        if (handler instanceof ChannelOutboundHandler) {
-            ChannelOutboundHandler h = (ChannelOutboundHandler) handler;
         try {
-                h.freeOutboundBuffer(this);
+            if (handler instanceof ChannelOutboundHandler) {
+                ((ChannelOutboundHandler) handler).freeOutboundBuffer(this);
+            }
         } catch (Throwable t) {
             notifyHandlerException(t);
         } finally {
             freeOutbound();
         }
-        }
 
         if (prev != null) {
             findContextOutbound().invokeFreeOutboundBuffer();