Fixed segmentation fault no global controller set POpenFOAMReader
Summary
Decomposed OpenFOAM cases cause Segmentation fault when read using python API.
This resolves #18143 (closed).
Problem
As @mwestphal stated, when no default global controller is set the Controller attribute is still pointing to nullptr
causing a segmentation fault.
Solution
Set the Controller to a new DummyController when no global controller is set.