python, java: Avoid bogus -fanalyzer warnings

This is essentially the same as the previous OCaml commit.  It does
not fix a real bug.

python/handle.c

@@ -88,7 +88,7 @@ guestfs_int_py_close (PyObject *self, PyObject *args)
   guestfs_close (g);
   Py_END_ALLOW_THREADS;
 
-  if (len > 0) {
+  if (callbacks && len > 0) {
     size_t i;
     for (i = 0; i < len; ++i)
       Py_XDECREF (callbacks[i]);