GateScheduleCanvasVisualizer: fix runtime error on Windows

The "displayTime=..." line produced simtime overflow error,
because indexStart was bogus a huge positive integer.

It was computed as:

auto indexStart = (int)... * durations.size();

which is signed * unsigned multiplication, whose result was signed on Linux,
and unsigned on Windows.

Workaround: factor out durations.size() as int numDurations, to eliminate
mixed-sign multiplications in the code. Also, make indexStart / indexEnd
explicit signed int.

src/inet/visualizer/canvas/common/GateScheduleCanvasVisualizer.cc

@@ -80,7 +80,8 @@ void GateScheduleCanvasVisualizer::refreshGateVisualization(const GateVisualizat
     auto durations = gate->getDurations();
     bool open = gate->getInitiallyOpen();
     clocktime_t scheduleDuration = 0;
-    for (size_t i = 0; i < durations.size(); i++)
+    int numDurations = (int)durations.size();  // make it signed, to avoid mixed-sign multiplications in the code below
+    for (int i = 0; i < numDurations; i++)
         scheduleDuration += durations[i];
     if (scheduleDuration == 0)
         figure->addSchedule(0, width, open);
@@ -90,12 +91,12 @@ void GateScheduleCanvasVisualizer::refreshGateVisualization(const GateVisualizat
         clocktime_t schedulePosition = std::fmod((currentTime + gate->getInitialOffset()).dbl(), scheduleDuration.dbl());
         auto scheduleDisplayStart = schedulePosition - (currentTimePosition / width) * displayDuration;
         auto scheduleDisplayEnd = scheduleDisplayStart + displayDuration;
-        int indexStart = (int)std::floor(scheduleDisplayStart.dbl() / scheduleDuration.dbl()) * durations.size();
-        int indexEnd = (int)std::ceil(scheduleDisplayEnd.dbl() / scheduleDuration.dbl()) * durations.size();
-        clocktime_t displayTime = currentTime - schedulePosition + indexStart / (int)durations.size() * scheduleDuration;
+        int indexStart = (int)std::floor(scheduleDisplayStart.dbl() / scheduleDuration.dbl()) * numDurations;
+        int indexEnd = (int)std::ceil(scheduleDisplayEnd.dbl() / scheduleDuration.dbl()) * numDurations;
+        clocktime_t displayTime = currentTime - schedulePosition + indexStart / numDurations * scheduleDuration;
         figure->clearSchedule();
         for (int i = indexStart; i <= indexEnd; i++) {
-            auto duration = durations[(i + durations.size()) % durations.size()];
+            auto duration = durations[(i + numDurations) % numDurations];
             clocktime_t startTime = displayTime - currentTime;
             clocktime_t endTime = displayTime + duration - currentTime;
             double factor = width / displayDuration.dbl();