Fix Numpy 1.20.0 by initializing PyArray_Descr portably

Description

According to the Numpy documentation:

To ensure compatibility:

• Never declare a non-pointer instance of the struct
• Never perform pointer arithmatic
• Never use sizof(PyArray_Descr)

The SWIG bindings broke the first of these rules. Improper order of initialization led to a null pointer that was causing a segfault.

Fixes #414 (closed). (We shall see!)

API Changes and Justification

Backwards Compatible Changes

• This change introduces no API changes
• This change adds new API calls

Backwards Incompatible Changes

• This change modifies an existing API
• This change removes an existing API

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

N/A

lal/swig/SWIGPython.i

@@ -676,6 +676,7 @@ SWIGINTERN bool swiglal_release_parent(void *ptr) {
         | NPY_ITEM_IS_POINTER | NPY_NEEDS_INIT | NPY_NEEDS_PYAPI;
       (*pdescr)->f = &swiglal_py_array_objview_##ACFTYPE##_arrfuncs;
       if (PyArray_RegisterDataType(*pdescr) < 0) {
+        PyErr_Print();  // FIXME: remove before merging
         return NULL;
       }
     }