Part: Fix several coverity issues:

* CID 350581: Structurally dead code
* CID 350620: Structurally dead code
* CID 350563: Big parameter passed by value
* CID 350552: Uncaught exception
* CID 305193: Uncaught exception
* CID 350556: Uninitialized scalar field
* CID 350579: Uninitialized pointer read

src/Mod/Part/App/GeometrySurfacePyImp.cpp

@@ -238,9 +238,6 @@ PyObject* GeometrySurfacePy::getDN(PyObject *args)
         PyErr_SetString(PartExceptionOCCError, e.GetMessageString());
         return nullptr;
     }
-
-    PyErr_SetString(PartExceptionOCCError, "Geometry is not a surface");
-    return nullptr;
 }
 
 PyObject* GeometrySurfacePy::value(PyObject *args)