Fix NPE when non chunked message with a large variable

src/main/java/org/jboss/netty/handler/codec/http/MixedFileUpload.java

@@ -62,8 +62,10 @@ public class MixedFileUpload implements FileUpload {
                         .getContentType(), fileUpload
                         .getContentTransferEncoding(), fileUpload.getCharset(),
                         definedSize);
-                diskFileUpload.addContent(((MemoryFileUpload) fileUpload)
+                if (((MemoryFileUpload) fileUpload).getChannelBuffer() != null){
+                    diskFileUpload.addContent(((MemoryFileUpload) fileUpload)
                         .getChannelBuffer(), last);
+                }
                 fileUpload = diskFileUpload;
             }
         }