[rpc] Mention that HD is enabled if hdmasterkeyid is present

Author: fanquake

src/wallet/rpcwallet.cpp

@@ -2768,7 +2768,7 @@ UniValue getwalletinfo(const JSONRPCRequest& request)
             "  \"keypoolsize_hd_internal\": xxxx, (numeric) how many new keys are pre-generated for internal use (used for change outputs, only appears if the wallet is using this feature, otherwise external keys are used)\n"
             "  \"unlocked_until\": ttt,           (numeric) the timestamp in seconds since epoch (midnight Jan 1 1970 GMT) that the wallet is unlocked for transfers, or 0 if the wallet is locked\n"
             "  \"paytxfee\": x.xxxx,              (numeric) the transaction fee configuration, set in " + CURRENCY_UNIT + "/kB\n"
-            "  \"hdmasterkeyid\": \"<hash160>\"     (string) the Hash160 of the HD master pubkey\n"
+            "  \"hdmasterkeyid\": \"<hash160>\"     (string, optional) the Hash160 of the HD master pubkey (only present when HD is enabled)\n"
             "}\n"
             "\nExamples:\n"
             + HelpExampleCli("getwalletinfo", "")