Revert the change that tries to zero out a closure's result storage

area because the size if unknown in source/callproc.c.

Modules/_ctypes/callbacks.c

@@ -205,24 +205,14 @@ if (x == NULL) _AddTraceback(what, __FILE__, __LINE__ - 1), PyErr_Print()
 
 	result = PyObject_CallObject(callable, arglist);
 	CHECK("'calling callback function'", result);
-#ifdef WORDS_BIGENDIAN
-	/* See the corresponding code in callproc.c, around line 961 */
-	if (restype->type != FFI_TYPE_FLOAT && restype->size < sizeof(ffi_arg))
-		mem = (char *)mem + sizeof(ffi_arg) - restype->size;
-#endif
-	/* The code that converts 'result' into C data is not executed when
-	   'callable' returns Py_None, so we zero out the memory that will
-	   receive the C return data to not return random data.
-
-	   Cleaner would be to call 'setfunc' anyway and complain with
-	   PyErr_WriteUnraisable(), but ctypes has always accepted a Py_None
-	   return value for *any* 'restype' and it would probably break too
-	   much code if this is changed now.
-	 */
-	memset(mem, 0, restype->size);
 	if ((restype != &ffi_type_void) && result && result != Py_None) {
 		PyObject *keep;
 		assert(setfunc);
+#ifdef WORDS_BIGENDIAN
+		/* See the corresponding code in callproc.c, around line 961 */
+		if (restype->type != FFI_TYPE_FLOAT && restype->size < sizeof(ffi_arg))
+			mem = (char *)mem + sizeof(ffi_arg) - restype->size;
+#endif
 		keep = setfunc(mem, result, 0);
 		CHECK("'converting callback result'", keep);
 		/* keep is an object we have to keep alive so that the result