Fix asyncpg with Py_DEBUG mode (MagicStack#719)

If Py_DEBUG enabled, then newly allocated memory is filled with the byte 0xCD (CLEANBYTE) https://docs.python.org/3/c-api/memory.html#c.PyMem_SetupDebugHooks This breaks checks for `pointer == NULL` and results in crash. From documentation PyObject_GC_Track https://docs.python.org/3/c-api/gcsupport.html#c.PyObject_GC_Track: > This should be called once all the fields followed by the tp_traverse > handler become valid, usually near the end of the constructor.

Author: shadchin

asyncpg/protocol/record/recordobj.c

@@ -31,6 +31,7 @@ ApgRecord_New(PyTypeObject *type, PyObject *desc, Py_ssize_t size)
 {
  ApgRecordObject *o;
  Py_ssize_t i;
+ int need_gc_track = 0;
 
  if (size < 0 || desc == NULL || !ApgRecordDesc_CheckExact(desc)) {
  PyErr_BadInternalCall();
@@ -54,7 +55,7 @@ ApgRecord_New(PyTypeObject *type, PyObject *desc, Py_ssize_t size)
  }
  }
 
- PyObject_GC_Track(o);
+ need_gc_track = 1;
  } else {
  assert(PyType_IsSubtype(type, &ApgRecord_Type));
 
@@ -78,6 +79,9 @@ ApgRecord_New(PyTypeObject *type, PyObject *desc, Py_ssize_t size)
  Py_INCREF(desc);
  o->desc = (ApgRecordDescObject*)desc;
  o->self_hash = -1;
+ if (need_gc_track) {
+ PyObject_GC_Track(o);
+ }
  return (PyObject *) o;
 }