Client: allow to decode data several times

Data contains a pair of iterators, which are considered to be light -
let's copy iterator before decoding data to allow to decode the same
data several times (or it can be decoded, and then encoded to send to
another tarantool from router).

Author: drewdzzz

src/Client/ResponseReader.hpp

@@ -104,7 +104,10 @@ struct Data {
 	template<class T>
 	bool decode(T& tuples)
 	{
-		return mpp::decode(iters.first, tuples);
+		it_t itr = iters.first;
+		bool ok = mpp::decode(itr, tuples);
+		assert(itr == iters.second);
+		return ok;
 	}
 
 	static constexpr auto mpp = &Data<BUFFER>::iters;