Merge patch series "Improve pid_nr_ns()"

In various places pid_nr_ns() can be called with a NULL pointer.
Fix those up and improve pid_nr_ns() callers.

Link: https://lore.kernel.org/20250802022123.3536934-1-gxxa03070307@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>