Fix bug in getrescaninfo

There was a small bug in getrescaninfo where when a rescan first starts, it
shows rescanning=true but progress=100% because rescanHeight was not initialized
correctly.

Also update our rescanHeight while we are fast-forwarding thru blocks which are
before the current wallet birthday.

src/wallet/wallet.cpp

@@ -2763,13 +2763,16 @@ int CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, bool fUpdate)
     pwalletMain->fRescanning = true;
     CBlockIndex* pindex = pindexStart;
     pwalletMain->rescanStartHeight = pindex->GetHeight();
+    pwalletMain->rescanHeight      = pwalletMain->rescanStartHeight;
     {
         LOCK2(cs_main, cs_wallet);
 
         // no need to read and scan block, if block was created before
         // our wallet birthday (as adjusted for block time variability)
-        while (pindex && nTimeFirstKey && (pindex->GetBlockTime() < (nTimeFirstKey - 7200)))
+        while (pindex && nTimeFirstKey && (pindex->GetBlockTime() < (nTimeFirstKey - 7200))) {
             pindex = chainActive.Next(pindex);
+            pwalletMain->rescanHeight = pindex->GetHeight();
+        }
 
         ShowProgress(_("Rescanning..."), 0); // show rescan progress in GUI as dialog or on splashscreen, if -rescan on startup
         double dProgressStart = Checkpoints::GuessVerificationProgress(chainParams.Checkpoints(), pindex, false);
@@ -2777,7 +2780,6 @@ int CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, bool fUpdate)
 
         while (pindex)
         {
-            pwalletMain->rescanHeight = pindex->GetHeight();
             if (pindex->GetHeight() % 100 == 0 && dProgressTip - dProgressStart > 0.0)
                 ShowProgress(_("Rescanning..."), std::max(1, std::min(99, (int)((Checkpoints::GuessVerificationProgress(chainParams.Checkpoints(), pindex, false) - dProgressStart) / (dProgressTip - dProgressStart) * 100))));
 
@@ -2821,6 +2823,8 @@ int CWallet::ScanForWalletTransactions(CBlockIndex* pindexStart, bool fUpdate)
                 nNow = GetTime();
                 LogPrintf("Still rescanning. At block %d. Progress=%f\n", pindex->GetHeight(), Checkpoints::GuessVerificationProgress(chainParams.Checkpoints(), pindex));
             }
+            // update rescan height before we scan the next block
+            pwalletMain->rescanHeight = pindex->GetHeight();
             pindex = chainActive.Next(pindex);
         }