Add missing optional.h include

Author: kristapsk

src/wallet/rpcwallet.cpp

@@ -8,6 +8,7 @@
 #include <interfaces/chain.h>
 #include <key_io.h>
 #include <node/context.h>
+#include <optional.h>
 #include <outputtype.h>
 #include <policy/feerate.h>
 #include <policy/fees.h>