fix bars initial animation

Author: beto-rodriguez

src/LiveChartsCore/CoreColumnSeries.cs

@@ -74,9 +74,7 @@ public override void Invalidate(Chart chart)
             secondaryScale, cartesianChart, this, secondaryAxis, primaryScale.ToPixels(pivot),
             cartesianChart.DrawMarginLocation.Y,
             cartesianChart.DrawMarginLocation.Y + cartesianChart.DrawMarginSize.Height, isStacked, false);
-        var pHelper = previousSecondaryScale == null || previousPrimaryScale == null
-            ? null
-            : new MeasureHelper(
+        var pHelper = new MeasureHelper(
                 previousSecondaryScale, cartesianChart, this, secondaryAxis, previousPrimaryScale.ToPixels(pivot),
                 cartesianChart.DrawMarginLocation.Y,
                 cartesianChart.DrawMarginLocation.Y + cartesianChart.DrawMarginSize.Height, isStacked, false);
@@ -161,7 +159,7 @@ public override void Invalidate(Chart chart)
                 var pi = helper.p;
                 var uwi = helper.uw;
 
-                if (previousSecondaryScale is not null && previousPrimaryScale is not null && pHelper is not null)
+                if (!isFirstDraw)
                 {
                     var previousPrimary = previousPrimaryScale.ToPixels(coordinate.PrimaryValue);
                     var bp = Math.Abs(previousPrimary - pHelper.p);

src/LiveChartsCore/CoreRowSeries.cs

@@ -79,9 +79,7 @@ public override void Invalidate(Chart chart)
             cartesianChart.DrawMarginLocation.X,
             cartesianChart.DrawMarginLocation.X + cartesianChart.DrawMarginSize.Width, isStacked, true);
 
-        var pHelper = previousSecondaryScale == null || previousPrimaryScale == null
-            ? null
-            : new MeasureHelper(
+        var pHelper = new MeasureHelper(
                 previousSecondaryScale, cartesianChart, this, secondaryAxis, previousPrimaryScale.ToPixels(pivot),
                 cartesianChart.DrawMarginLocation.X,
                 cartesianChart.DrawMarginLocation.X + cartesianChart.DrawMarginSize.Width, isStacked, true);
@@ -165,7 +163,7 @@ public override void Invalidate(Chart chart)
                 var pi = helper.p;
                 var uwi = helper.uw;
 
-                if (previousSecondaryScale is not null && previousPrimaryScale is not null && pHelper is not null)
+                if (!isFirstDraw)
                 {
                     var previousPrimary = previousPrimaryScale.ToPixels(coordinate.PrimaryValue);
                     var bp = Math.Abs(previousPrimary - pHelper.p);

src/LiveChartsCore/Kernel/Extensions.cs

@@ -505,7 +505,7 @@ public static Scaler GetNextScaler(this ICartesianAxis axis, CartesianChartEngin
     /// <param name="axis"></param>
     /// <param name="chart"></param>
     /// <returns></returns>
-    public static Scaler? GetActualScaler(this ICartesianAxis axis, CartesianChartEngine chart)
+    public static Scaler GetActualScaler(this ICartesianAxis axis, CartesianChartEngine chart)
     {
         // returns an scaler with the "Motion bounds", which means the bounds but tracked by the motion canvas
         // clock, so this returns the bounds that are being animated at the moment this method is called.