Description of problem:
SDL2 crashes in wayland_get_system_cursor when hovering mouse over checkbox in 'boguex 0' application.

Version-Release number of selected component (if applicable):


How reproducible:
Always

Steps to Reproduce:
1. boguex 0
2. hover over checkbox
3. crash

Actual results:

I don't have a minimal C repro for this, but 'boguex 0' (an OCaml application using SDL2) reproduces this easily as soon as you hover the mouse over the checkbox:
```
Thread 1 "boguex" received signal SIGSEGV, Segmentation fault.
0x00007ffff7ee5280 in wayland_get_system_cursor (scale=<synthetic pointer>, cdata=0x165dcb0, vdata=<optimized out>) at /usr/src/debug/SDL2-2.26.0-1.fc37.x86_64/src/video/wayland/SDL_waylandmouse.c:283
283	    cdata->buffer = WAYLAND_wl_cursor_image_get_buffer(cursor->images[0]);

(gdb) bt
#0  0x00007ffff7ee5280 in wayland_get_system_cursor (scale=<synthetic pointer>, cdata=0x165dcb0, vdata=<optimized out>)
    at /usr/src/debug/SDL2-2.26.0-1.fc37.x86_64/src/video/wayland/SDL_waylandmouse.c:283
#1  Wayland_ShowCursor (cursor=<optimized out>) at /usr/src/debug/SDL2-2.26.0-1.fc37.x86_64/src/video/wayland/SDL_waylandmouse.c:516
#2  0x00007ffff7d9c6d6 in ffi_call_unix64 () at ../src/x86/unix64.S:105
#3  0x00007ffff7d99492 in ffi_call_int
    (cif=<optimized out>, fn=<optimized out>, rvalue=<optimized out>, avalue=<optimized out>, closure=<optimized out>) at ../src/x86/ffi64.c:672
#4  0x0000000000604ec1 in ctypes_call
    (fnname=<optimized out>, function=<optimized out>, callspec_=<optimized out>, argwriter=<optimized out>, rvreader=<optimized out>)
    at /var/home/edwin/.opam/5.0.0/.opam-switch/build/ctypes.0.20.1/src/ctypes-foreign/ffi_call_stubs.c:404
#5  0x000000000063700b in <signal handler called> ()
#6  0x00000000005707a0 in camlCtypes_ffi__fun_1348 () at src/ctypes-foreign/ctypes_ffi.ml:111
#7  0x000000000050afdd in camlBogue__B_main__check_mouse_motion_3565 () at lib/b_main.ml:327
#8  0x000000000050dd3c in camlBogue__B_main__loop_3763 () at lib/b_main.ml:850
#9  0x000000000050e0be in camlBogue__B_main__one_step_3773 () at lib/b_main.ml:882
#10 0x000000000050eb6a in camlBogue__B_main__loop_3871 () at lib/b_main.ml:1045
#11 0x000000000050ea0c in camlBogue__B_main__run_3865 () at lib/b_main.ml:1049
#12 0x00000000005a71f0 in camlStdlib__List__iter_508 () at list.ml:110
#13 0x00000000004b0b98 in camlDune__exe__Example__entry () at examples/example.ml:1298
#14 0x0000000000498b7b in caml_program ()
#15 0x00000000006370c4 in <signal handler called> ()
#16 0x0000000000636a86 in caml_startup_common (pooling=<optimized out>, argv=0x7fffffffdc58) at runtime/startup_nat.c:129
#17 caml_startup_common (argv=0x7fffffffdc58, pooling=<optimized out>) at runtime/startup_nat.c:85
#18 0x0000000000636afb in caml_startup_exn (argv=<optimized out>) at runtime/startup_nat.c:136
#19 caml_startup (argv=<optimized out>) at runtime/startup_nat.c:141
#20 caml_main (argv=<optimized out>) at runtime/startup_nat.c:148
#21 0x000000000049821c in main (argc=<optimized out>, argv=<optimized out>) at runtime/main.c:37
```

Unfortunately a lot of the values are optimized out, but I confirmed in gdb that trying to retrieve the cursor gives NULL, and there are no NULL pointer checks in the code:
```
(gdb) up
#1  Wayland_ShowCursor (cursor=<optimized out>) at /usr/src/debug/SDL2-2.26.0-1.fc37.x86_64/src/video/wayland/SDL_waylandmouse.c:516
516	            if (!wayland_get_system_cursor(d, data, &scale)) {
(gdb) print *data
$4 = {buffer = 0x0, surface = 0x165dcf0, hot_x = 0, hot_y = 0, w = 0, h = 0, system_cursor = SDL_SYSTEM_CURSOR_HAND, shm_data = 0x0}
(gdb) down
#0  0x00007ffff7ee5280 in wayland_get_system_cursor (scale=<synthetic pointer>, cdata=0x165dcb0, vdata=<optimized out>)
    at /usr/src/debug/SDL2-2.26.0-1.fc37.x86_64/src/video/wayland/SDL_waylandmouse.c:283
283	    cdata->buffer = WAYLAND_wl_cursor_image_get_buffer(cursor->images[0]);
(gdb) call WAYLAND_wl_cursor_theme_get_cursor(theme, "hand2")
$5 = (struct wl_cursor *) 0x0
```

Workaround is to use X11 driver which doesn't have these problems.

Expected results:
No crash

Additional info:
I think the following upstream commit would fix this already:
https://github.com/libsdl-org/SDL/commit/5a4283134542d4bdb3d968a836387a750ce80517

I confirmed in gdb that I do get a valid cursor pointer with the call from that patch.