Issue #10253: FileIO leaks a file descriptor when trying to open a file
for append that isn't seekable.  Patch by Brian Brazil.
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 16b98d6..279df34 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -396,8 +396,13 @@
            end of file (otherwise, it might be done only on the
            first write()). */
         PyObject *pos = portable_lseek(self->fd, NULL, 2);
-        if (pos == NULL)
+        if (pos == NULL) {
+            if (closefd) {
+                close(self->fd);
+                self->fd = -1;
+            }
             goto error;
+        }
         Py_DECREF(pos);
     }