signrawtransaction: validate private key.

src/rpcrawtransaction.cpp

@@ -587,6 +587,8 @@ Value signrawtransaction(const Array& params, bool fHelp)
             if (!fGood)
                 throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key");
             CKey key = vchSecret.GetKey();
+            if (!key.IsValid())
+                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Private key outside allowed range");
             tempKeystore.AddKey(key);
         }
     }