Add assertion and cast before sending reject code

This gets rid of a warning. Add an assertion to make sure that the
reject code is in the correct range for the network protocol
(if it is outside the range it must be a bug)

src/main.cpp

@@ -1343,7 +1343,8 @@ void static InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state
     if (state.IsInvalid(nDoS)) {
         std::map<uint256, NodeId>::iterator it = mapBlockSource.find(pindex->GetBlockHash());
         if (it != mapBlockSource.end() && State(it->second)) {
-            CBlockReject reject = {state.GetRejectCode(), state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), pindex->GetBlockHash()};
+            assert(state.GetRejectCode() < 0x100);
+            CBlockReject reject = {(unsigned char)state.GetRejectCode(), state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), pindex->GetBlockHash()};
             State(it->second)->rejects.push_back(reject);
             if (nDoS > 0)
                 Misbehaving(it->second, nDoS);