Fix a encoding struct bug in the compact protocol implementation to lua

code in lib/lua/TCompactProtocol.lua as follow:

function TCompactProtocol:writeStructBegin(name)
self.lastFieldIndex = self.lastFieldIndex + 1
self.lastField[self.lastFieldIndex] = self.lastFieldId
self.lastFieldId = 0
end

the lastFieldId is saved into the new lastFieldIndex pos and then is restored mistakenly later.