SIGSEGV with vtkFieldData::DeepCopy
The following python script causes SIGSEGV. It was confirmed with VTK8.2.
```
import vtk
f = vtk.vtkFieldData()
f.AddArray(vtk.vtkStringArray())
f0 = vtk.vtkFieldData()
f0.AddArray(vtk.vtkStringArray())
f.AddArray(vtk.vtkStringArray())
# f.Initialize()
f.DeepCopy(f0)
print(f.GetNumberOfArrays())
```
It prints "3", and then crashes in `vtkFieldData::~vtkFieldData()`.
It runs ok with output "1" if `f.Initialize()` is uncommented. It
seems that `this->Initialize()` is necessary at the beginning of
`vtkFieldData::DeepCopy`.
issue