minor fixes

Modules/_testcapimodule.c

@@ -861,6 +861,7 @@ pending_threadfunc(PyObject *self, PyObject *arg, PyObject *kwargs)
     unsigned int num_added = 0;
     for (; num_added < num; num_added++) {
         if (Py_AddPendingCall(&_pending_callback, callable) < 0) {
+            // out of memory and freelist is empty
             break;
         }
     }

Python/ceval_gil.c

@@ -1085,6 +1085,8 @@ Py_MakePendingCalls(void)
 void
 _PyEval_InitState(PyInterpreterState *interp)
 {
+    // Fill the pending freelist so that signal handlers can safely
+    // add pending calls without needing to allocate memory.
     struct _pending_calls *pending = &interp->ceval.pending;
     PyMutex_Lock(&pending->mutex);
     fill_pending_freelist(pending);