libobs: Fix Wayland segfault on shutdown

[joepadmiraal]

Description

The keyboard_listener events can still be triggered after obs_nix_wayland_hotkeys_platform_free has been called, resulting in a segfault inside rebuild_keymap_data. Add a call to wl_keyboard_release to prevent new events from being triggered.

Motivation and Context

I was running OBS 32.1.2 on Ubuntu26.04 and when I closed it the app crashed.
An Ubuntu Apport dialog appeared and after investigating the core dump I found the issue.

#0  xkb_keymap_key_get_syms_by_level()       libxkbcommon      <-- SIGSEGV
#1  load_keymap_data()                       libobs           (obs-nix-wayland.c:48-67)
#2  xkb_keymap_key_for_each()                libxkbcommon     (iterates keymap, calls #1)
#3  libffi
#4  libffi
#5  ffi_call()                               libffi           (Wayland invokes the listener)
#6  libwayland-client
#7  libwayland-client
#8  wl_display_dispatch_queue_pending()      libwayland-client
#9  QtWaylandClient::QWaylandDisplay::flushRequests()
#10 QEventDispatcherGlib::processEvents()    libQt6Core
#11 QEventLoop::exec()                       libQt6Core
#12 QCoreApplication::exec()                 libQt6Core
#13 obs main

How Has This Been Tested?

Since this is a race condition its very hard to reproduce.
I let Claude make a reproduction with a copy of the relevant code from obs-nix-wayland.c and verified with AddressSanitizer.

After the fix I also compiled OBS and ran it couple of times to see if no new shutdown errors appeared.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have read the contributing document.
• My code has been run through clang-format.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.