Fix infinity checks.

Misread `std::isfinite` in C++ code as `std::infinite`, ha.

src/Avalonia.Controls/Repeaters/FlowLayoutAlgorithm.cs

@@ -337,7 +337,7 @@ namespace Avalonia.Controls.Repeaters
                             // Does not fit, wrap to the previous row
                             var availableSizeMinor = _orientation.Minor(availableSize);
 
-                            _orientation.SetMinorStart(ref currentBounds, double.IsInfinity(availableSizeMinor) ? availableSizeMinor - _orientation.Minor(desiredSize) : 0);
+                            _orientation.SetMinorStart(ref currentBounds, !double.IsInfinity(availableSizeMinor) ? availableSizeMinor - _orientation.Minor(desiredSize) : 0);
                             _orientation.SetMajorStart(ref currentBounds, lineOffset - _orientation.Major(desiredSize) - lineSpacing);
 
                             if (lineNeedsReposition)

src/Avalonia.Controls/Repeaters/StackLayout.cs

@@ -97,7 +97,7 @@ namespace Avalonia.Controls.Repeaters
         {
             var measureSizeMinor = _orientation.Minor(measureSize);
             return _orientation.MinorMajorSize(
-                double.IsInfinity(measureSizeMinor) ?
+                !double.IsInfinity(measureSizeMinor) ?
                     Math.Max(measureSizeMinor, _orientation.Minor(desiredSize)) :
                     _orientation.Minor(desiredSize),
                 _orientation.Major(desiredSize));