Properly update PlotPoints cache.

This commit adds the UpdateCache method to the vtkPlotPoints class,
which will properly update its cache when necessary
(e.g. when the log scale is activated on one of its axes).

Charts/Core/vtkPlotPoints.cxx

@@ -637,6 +637,14 @@ bool vtkPlotPoints::GetDataArrays(vtkTable* table, vtkDataArray* array[2])
   return true;
 }
 
+//------------------------------------------------------------------------------
+void vtkPlotPoints::UpdateCache()
+{
+  // Update has the necessary checks in place and will update the
+  // ValidPointMask and TableCache when necessary.
+  this->Update();
+}
+
 //------------------------------------------------------------------------------
 bool vtkPlotPoints::UpdateTableCache(vtkTable* table)
 {

Charts/Core/vtkPlotPoints.h

@@ -193,6 +193,11 @@ protected:
    */
   bool GetDataArrays(vtkTable* table, vtkDataArray* array[2]);
 
+  /**
+   * Update the table cache if necessary.
+   */
+  virtual void UpdateCache() override;
+
   /**
    * Update the table cache.
    */