BUG 13312: Fix crash on vtkImageProperty DeepCopy with LUT.

If DeepCopy was used to copy a vtkImageProperty with a LookupTable into
a vtkImageProperty without a LookupTable, a segmentation fault occurred.

Backport of 316062ca from master to release.

Change-Id: I1039fd8c9109b9005ae9038b0404c103c141079a

Rendering/vtkImageProperty.cxx

@@ -91,9 +91,8 @@ void vtkImageProperty::DeepCopy(vtkImageProperty *p)
       }
     else
       {
-      vtkScalarsToColors *olut = this->GetLookupTable();
-      vtkScalarsToColors *nlut = olut->NewInstance();
-      nlut->DeepCopy(olut);
+      vtkScalarsToColors *nlut = lut->NewInstance();
+      nlut->DeepCopy(lut);
       this->SetLookupTable(nlut);
       nlut->Delete();
       }