Fix memory leak in vtkSelectionSource

This free's the memory for the QueryString in
vtkSelectionSource's destructor.

Change-Id: Ic3d0cbab119f263836cb4a258704b3ccab7d2ff1

Graphics/vtkSelectionSource.cxx

@@ -80,6 +80,7 @@ vtkSelectionSource::~vtkSelectionSource()
     {
     delete[] this->ArrayName;
     }
+  delete[] this->QueryString;
 }
 
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