gh-105375: Improve error handling in _ctypes

Prevent repeated PyLong_FromVoidPtr() from possibly overwriting the
current exception.

Author: erlend-aasland

Misc/NEWS.d/next/Library/2023-06-09-21-40-45.gh-issue-105375._sZilh.rst

@@ -0,0 +1 @@
+Fix bugs in :mod:`_ctypes` where exceptions could end up being overwritten.

Modules/_ctypes/callbacks.c

@@ -479,13 +479,20 @@ long Call_GetClassObject(REFCLSID rclsid, REFIID riid, LPVOID *ppv)
 
     {
         PyObject *py_rclsid = PyLong_FromVoidPtr((void *)rclsid);
+        if (py_rclsid == NULL) {
+            PyErr_WriteUnraisable(context ? context : Py_None);
+            return E_FAIL;
+        }
         PyObject *py_riid = PyLong_FromVoidPtr((void *)riid);
+        if (py_riid == NULL) {
+            Py_DECREF(py_rclsid);
+            PyErr_WriteUnraisable(context ? context : Py_None);
+            return E_FAIL;
+        }
         PyObject *py_ppv = PyLong_FromVoidPtr(ppv);
-        if (!py_rclsid || !py_riid || !py_ppv) {
-            Py_XDECREF(py_rclsid);
-            Py_XDECREF(py_riid);
-            Py_XDECREF(py_ppv);
-            Py_DECREF(func);
+        if (py_ppv == NULL) {
+            Py_DECREF(py_rclsid);
+            Py_DECREF(py_riid);
             PyErr_WriteUnraisable(context ? context : Py_None);
             return E_FAIL;
         }