Merge #1206: [BUG][RPC] fix signature check (against old format) in m…

…nbudgetrawvote

ae063d0 [BUG][RPC] fix signature check (against old format) in mnbudgetrawvote (random-zebra)

Pull request description:

  `CBudgetVote` object in `mnbudgetrawvote` is initialized with default nMessVersion (`MessageVersion::MESS_VER_HASH`). Thus the signature validation fails when the user provides an external signature performed over the old message format.

ACKs for top commit:
  Fuzzbawls:
    utACK ae063d0
  furszy:
    utACK ae063d0

Tree-SHA512: 16281277c001521ace380eada664138fa88f8a4fc93533427893ca6ab9ed56221962264859ea1b5c4d2aa751931dbfb90bfc46523beb705e8801e739fa2f1f97

src/rpc/budget.cpp

@@ -729,7 +729,9 @@ UniValue mnbudgetrawvote(const UniValue& params, bool fHelp)
     vote.SetVchSig(vchSig);
 
     if (!vote.CheckSignature(true)) {
-        return "Failure to verify signature.";
+        // try old message version
+        vote.nMessVersion = MessageVersion::MESS_VER_STRMESS;
+        if (!vote.CheckSignature(true)) return "Failure to verify signature.";
     }
 
     std::string strError = "";