Checksum detection fix doesn't work with EventDataWrapper

[tharanga]

The fix for #256 (commit 68c0ec7) fails when we set NullEventDataDeserializer for format descriptor events. Attached is the patch to a test which triggers this failure.

EventDataWrapper.deserialize() method reads the whole inputStream which leads to this failure in EventDeserializer. This doesn't happen with FormatDescriptionEventData as that deserialize method just read required parts from inputStream instead of the whole stream.

null_format.txt

[tharanga]

+1 @shyiko !