Fix division by zero in time remaining

src/qt/modaloverlay.cpp

@@ -99,15 +99,18 @@ void ModalOverlay::tipUpdate(int count, const QDateTime& blockDate, double nVeri
                 progressDelta = progressStart-sample.second;
                 timeDelta = blockProcessTime[0].first - sample.first;
                 progressPerHour = progressDelta/(double)timeDelta*1000*3600;
-                remainingMSecs = remainingProgress / progressDelta * timeDelta;
+                remainingMSecs = (progressDelta > 0) ? remainingProgress / progressDelta * timeDelta : -1;
                 break;
             }
         }
         // show progress increase per hour
         ui->progressIncreasePerH->setText(QString::number(progressPerHour*100, 'f', 2)+"%");
 
-        // show expected remaining time
+        if(remainingMSecs >= 0) {	
             ui->expectedTimeLeft->setText(GUIUtil::formatNiceTimeOffset(remainingMSecs / 1000.0));
+        } else {
+            ui->expectedTimeLeft->setText(QObject::tr("unknown"));
+        }
 
         static const int MAX_SAMPLES = 5000;
         if (blockProcessTime.count() > MAX_SAMPLES)