readline: backport a patch to fix for caller setting rl_prompt to NULL

readline: backport a patch to fix for caller setting rl_prompt to NULL

I've observed this issue affecting iwctl and connmanctl.

Patching readline solves the issue.

The original patch from [5] mixes many fixes in one commit. I've extract
only what matters to solve the issues observed with connman and iwd. The
final patch is the same patch sent by readline author to readline's mail list [6].

References:

1: https://gitlab.archlinux.org/archlinux/packaging/packages/readline/-/issues/1
2: https://gitlab.archlinux.org/archlinux/packaging/packages/readline/-/commit/b30636dc66fc783a091af51b049dc5240f861dd0
3: https://lists.gnu.org/archive/html/bug-readline/2025-07/msg00007.html
4: https://lore.kernel.org/connman/20251018212411.181909-1-jsbronder@cold-front.org/
5: https://cgit.git.savannah.gnu.org/cgit/readline.git/commit/display.c?h=devel&id=488d7edc22894d30b6de7f2d4190bf7403f63ffd
6: https://lists.gnu.org/archive/html/bug-readline/2025-07/txtmA7rksnmmi.txt

Fixes [YOCTO #16047]

CC  Paul Barker <paul@pbarker.dev>

CC: Jose Quaresma <quaresma.jose@gmail.com>
CC: Khem Raj <raj.khem@gmail.com>
Signed-off-by: João Henrique Ferreira de Freitas <joaohf@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>