On pointer enter notification, Xwayland checks for an existing pointer
warp with a `NULL` sprite.
In turn, `xwl_pointer_warp_emulator_maybe_lock()` checks for an existing
grab and the destination window using `XYToWindow()` which does not
check for the actual sprite not being `NULL`.
So, in some cases, when the pointer enters the surface and there is an
existing X11 grab which is not an ownerEvents grab, Xwayland would crash
trying to dereference the `NULL` sprite pointer:
#0 __GI_raise ()
#1 __GI_abort () at abort.c:79
#2 OsAbort () at utils.c:1351
#3 AbortServer () at log.c:879
#4 FatalError () at log.c:1017
#5 OsSigHandler () at osinit.c:156
#6 OsSigHandler () at osinit.c:110
#7 <signal handler called>
#8 XYToWindow (pSprite=0x0, x=0, y=0) at events.c:2880
#9 xwl_pointer_warp_emulator_maybe_lock () at xwayland-input.c:2673
#10 pointer_handle_enter () at xwayland-input.c:434
Avoid the crash by simply checking for the sprite being not `NULL` in
`xwl_pointer_warp_emulator_maybe_lock()`
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Bugzilla: https://bugzilla.redhat.com/1708119
0a07446318