Don't DECREF the ctypes error_object without the GIL held.

Modules/_ctypes/callproc.c

@@ -834,11 +834,11 @@ static int _call_function_pointer(int flags,
         space[0] = errno;
         errno = temp;
     }
-    Py_XDECREF(error_object);
 #ifdef WITH_THREAD
     if ((flags & FUNCFLAG_PYTHONAPI) == 0)
         Py_BLOCK_THREADS
 #endif
+    Py_XDECREF(error_object);
 #ifdef MS_WIN32
 #ifndef DONT_USE_SEH
     if (dwExceptionCode) {