Merge bitcoin#15279: wallet: Clarify rescanblockchain doc

fa5e6ef wallet: Fixup rescanblockchain result doc (MarcoFalke)

Pull request description:

  This was probably accidentally added to the wrong line when addressing the feedback here: bitcoin#7061 (comment)

  I already added the default values in bitcoin#14877, but it could be clarified more that this really has no specific block height as default value, since the tip can change during a rescan.

Tree-SHA512: 48a3c5143e2b7129ee8f396d2e77550cb393fbe45f5936aeebeb7a201d61560336a3ae47b26bb757a4dbbe217e06abfd67a5a673aef266b6c4d7a80d049a2b49

src/wallet/rpcwallet.cpp

@@ -4105,11 +4105,11 @@ static UniValue rescanblockchain(const JSONRPCRequest& request)
             "\nRescan the local blockchain for wallet related transactions.\n"
             "\nArguments:\n"
             "1. \"start_height\"    (numeric, optional) block height where the rescan should start\n"
-            "2. \"stop_height\"     (numeric, optional) the last block height that should be scanned\n"
+            "2. \"stop_height\"     (numeric, optional) the last block height that should be scanned. If none is provided it will rescan up to the tip at return time of this call.\n"
             "\nResult:\n"
             "{\n"
-            "  \"start_height\"     (numeric) The block height where the rescan has started. If omitted, rescan started from the genesis block.\n"
-            "  \"stop_height\"      (numeric) The height of the last rescanned block. If omitted, rescan stopped at the chain tip.\n"
+            "  \"start_height\"     (numeric) The block height where the rescan has started.\n"
+            "  \"stop_height\"      (numeric) The height of the last rescanned block.\n"
             "}\n"
             "\nExamples:\n"
             + HelpExampleCli("rescanblockchain", "100000 120000")