Fix a UI freeze on 'finished' witness accounts

There was a regression causing the UI to freeze in an infinite loop due to a zero account weight for the 'finished' account.

Fix this in two seperate ways:
1) Use a fallback weight (if zero) so that any future bugs like this can't cause an infinite loop again
2) Remove the part of the code that was causing the regression - 'finished' accounts do still have a weight for 'UI' purposes, as this weight is used to populate the historical graphs

Also clean up/clarify a few comments in the code around this.

src/qt/_Gulden/witnessdialog.cpp

@@ -583,7 +583,7 @@ WitnessInfoForAccount WitnessDialog::GetWitnessInfoForAccount(CAccount* forAccou
     infoForAccount.nWitnessLength = infoForAccount.nOriginLength;
     if (infoForAccount.nOriginNetworkWeight == 0)
         infoForAccount.nOriginNetworkWeight = gStartingWitnessNetworkWeightEstimate;
-    uint64_t nEstimatedWitnessBlockPeriodOrigin = estimatedWitnessBlockPeriod(infoForAccount.nOriginWeight, infoForAccount.nOriginNetworkWeight);
+    uint64_t nEstimatedWitnessBlockPeriodOrigin = estimatedWitnessBlockPeriod((infoForAccount.nOriginWeight>0)?infoForAccount.nOriginWeight:gMinimumWitnessWeight, infoForAccount.nOriginNetworkWeight);
     infoForAccount.pointMapForecast[0] = 0;
     for (unsigned int i = nEstimatedWitnessBlockPeriodOrigin; i < infoForAccount.nWitnessLength; i += nEstimatedWitnessBlockPeriodOrigin)
     {

src/wallet/witness_operations.cpp

@@ -575,7 +575,7 @@ CWitnessAccountStatus GetWitnessAccountStatus(CWallet* pWallet, CAccount* accoun
         witnessInfo = GetWitnessInfoWrapper();
     }
 
-    // Collect uspent witnesses coins on for the account
+    // Collect uspent witnesses coins for the account
     std::vector<RouletteItem> accountItems;
     for (const auto& item : witnessInfo.witnessSelectionPoolUnfiltered)
     {
@@ -647,7 +647,7 @@ CWitnessAccountStatus GetWitnessAccountStatus(CWallet* pWallet, CAccount* accoun
         throw std::runtime_error("Unable to determine witness state.");
     }
 
-    // NOTE: assuming any unconfirmed tx here is a witness one to avoid getting the witness bundles and testing those, this will almost always be
+    // NOTE: assuming any unconfirmed tx here is a witness; avoid getting the witness bundles and testing those, this will almost always be
     // correct. Any edge cases where this fails will automatically resolve once the tx confirms.
     bool hasUnconfirmedWittnessTx = std::any_of(pWallet->mapWallet.begin(), pWallet->mapWallet.end(), [=](const auto& it){
         const auto& wtx = it.second;
@@ -667,7 +667,8 @@ CWitnessAccountStatus GetWitnessAccountStatus(CWallet* pWallet, CAccount* accoun
         account,
         status,
         networkWeight,
-        isLocked ? std::accumulate(accountItems.begin(), accountItems.end(), uint64_t(0), [](const uint64_t acc, const RouletteItem& ri){ return acc + ri.nWeight; }) : uint64_t(0),
+        //NB! We always want the account weight (even if expired) - otherwise how do we e.g. draw a historical graph of the expected earnings for the expired account?
+        std::accumulate(accountItems.begin(), accountItems.end(), uint64_t(0), [](const uint64_t acc, const RouletteItem& ri){ return acc + ri.nWeight; }),
         hasScriptLegacyOutput,
         hasUnconfirmedWittnessTx,
         nLockFromBlock,

src/wallet/witness_operations.h

@@ -99,8 +99,8 @@ struct CWitnessAccountStatus
 };
 
 /** Get account witness status and accompanying details
- * hasScriptLegacyOutput iff any of the outputs is CTxOutType::ScriptLegacyOutput
- * hasUnconfirmedWittnessTx iff unconfirmed witness tx for the account (not actually checked for witness type, see implementation note)
+ * hasScriptLegacyOutput IFF any of the outputs is CTxOutType::ScriptLegacyOutput
+ * hasUnconfirmedWittnessTx IFF unconfirmed witness tx for the account (not actually checked for witness type, see implementation note)
  * pWitnessInfo if != nullptr it will be filled with the witnessInfo if available
 */
 CWitnessAccountStatus GetWitnessAccountStatus(CWallet* pWallet, CAccount* account, CGetWitnessInfo* pWitnessInfo = nullptr);