vtkOpenGLGPUVolumeRayCastMapper: handle when table size increases

Because the texture table size is now dynamic, it's no longer sufficient to only
allocate it when the pointer is NULL. If the texture table has previously been
allocated and the computed table size increases, it's necessary to reallocate
the table, otherwise a memory error occurs.

Author: msmolens

Rendering/VolumeOpenGL/vtkOpenGLGPUVolumeRayCastMapper.cxx

@@ -368,10 +368,8 @@ class vtkOpacityTable: public vtkTextureTable
         {
         this->Loaded=false;
         const int tableSize = this->ComputeTableSize(scalarOpacity);
-        if(this->Table==0)
-          {
-          this->Table= new float[tableSize];
-          }
+        delete[] this->Table;
+        this->Table = new float[tableSize];
 
         scalarOpacity->GetTable(range[0],range[1],tableSize,this->Table);
 
@@ -524,11 +522,8 @@ class vtkRGBTable: public vtkTextureTable
         {
         this->Loaded=false;
         const int tableSize = this->ComputeTableSize(scalarRGB);
-
-        if(this->Table==0)
-          {
-          this->Table = new float[tableSize*3];
-          }
+        delete[] this->Table;
+        this->Table = new float[tableSize * 3];
 
         scalarRGB->GetTable(range[0],range[1],
                             tableSize,