BUG: Get rid of error printouts from TestRIBExporter

This fixes:
ERROR: In /Common/ExecutionModel/vtkImageAlgorithm.cxx, line 137
vtkOpenGLTexture (0x7fa67b434bc0): Definition of Execute() method should be in subclass and you should really use the ExecuteData(vtkInformation *request,...) signature instead

and

ERROR: In /home/danlipsa/src/VTK/IO/Image/vtkTIFFWriter.cxx, line 137
vtkTIFFWriter (0x2028280): Unsupported data type: double

ERROR: In /home/danlipsa/src/VTK/IO/Image/vtkTIFFWriter.cxx, line 248
vtkTIFFWriter (0x2028280): Could not get data from input.

ERROR: In /home/danlipsa/src/VTK/IO/Image/vtkTIFFWriter.cxx, line 410
vtkTIFFWriter (0x2028280): Problem writting trailer.

IO/Image/vtkTIFFWriter.cxx

@@ -37,6 +37,8 @@ vtkTIFFWriter::vtkTIFFWriter()
 //----------------------------------------------------------------------------
 void vtkTIFFWriter::Write()
 {
+  // make sure the latest input is available.
+  this->Update();
   this->SetErrorCode(vtkErrorCode::NoError);
   // Error checking
   if (this->GetInput() == NULL)

Rendering/Core/vtkTexture.h

@@ -212,6 +212,12 @@ protected:
   vtkTexture();
   ~vtkTexture();
 
+  // A texture is a sink, so there is no need to do anything.
+  // This definition avoids a warning when doing Update() on a vtkTexture object.
+  virtual void ExecuteData(vtkDataObject *)
+  {
+  }
+
   int Repeat;
   int EdgeClamp;
   int Interpolate;