The cursor colors are broken on big-endian systems. It seems that the
pipewire project always uses the RGBA format for cursors regardless the
platform used. At least the code in the `process_mouse_cursor_data` (resp.
`grd_spa_pixel_format_to_grd_pixel_format`) function relies on that. But
the `submit_cursor` function expects the colors to be in the ABGR format
on big-endian systems. Let's change the `submit_cursor` function to expect
the RGBA format also on the big-endian systems. This fixes the cursor
colors there.

Related: https://gitlab.gnome.org/GNOME/gnome-remote-desktop/-/issues/191

gnome-remote-desktop currently assumes, that the byte order for frames
is always BGRX, regardless of the machine type. While for little endian
machines, this is true, but on big endian machines, the frame type is
XRGB. So, fix this accordingly.

Closes: https://gitlab.gnome.org/GNOME/gnome-remote-desktop/-/issues/191

Currently, the first read operation of the session array is an
out-of-bounds read, and can thus make gnome-remote-desktop crash when
trying to get the session id from the uid.
This crash is especially hit, when no sessions are available.

Fix this issue by correctly setting the initial iterator value.

https://gitlab.gnome.org/GNOME/gnome-remote-desktop/-/merge_requests/251