Although not actually exploitable at the moment, a negative width/height
could make datasize wrap around and potentially lead to buffer overflow.
Since there is no reason a negative width/height is ever appropriate,
modify QEMUCursor struct and cursor_alloc prototype to accept uint16_t.
This protects us against accidentally introducing future bugs.

Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
Reported-by: Jacek Halon <jacek.halon@gmail.com>
Reported-by: Yair Mizrahi <yairh33@gmail.com>
Reported-by: Elsayed El-Refa'ei <e.elrefaei99@gmail.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230523163023.608121-1-mcascell@redhat.com>