Fix size method on anonymous mmap object

Author: aisk

Lib/test/test_mmap.py

@@ -506,6 +506,8 @@ def test_anonymous(self):
             m[x] = b
             self.assertEqual(m[x], b)
 
+        self.assertEqual(m.size(), PAGESIZE)
+
     def test_read_all(self):
         m = mmap.mmap(-1, 16)
         self.addCleanup(m.close)

Modules/mmapmodule.c

@@ -747,6 +747,9 @@ mmap_size_method(PyObject *op, PyObject *Py_UNUSED(ignored))
 
 #ifdef UNIX
     {
+        if (self->trackfd && self->fd == -1) {
+            return PyLong_FromSsize_t(self->size);
+        }
         struct _Py_stat_struct status;
         if (_Py_fstat(self->fd, &status) == -1)
             return NULL;