prevent integer overflow on 32 bit
prevent integer overflow on 32 bit

On 32 bit machine timespec->tv_sec (time_t) is 32 bit.
Also 1000 * 1000 * 1000 is 32 bit.
The multiplication of 2 32 bit integers gives a 32 bit integer, however
this can overflow.
Converting the first factor to 64 bit before the multiplication solves
the issue.

Signed-off-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>

SPICE/spice,ya-mouse/spice,ya-mouse/spice,fgouget/spice,fgouget/spice,ya-mouse/spice,fgouget/spice,SPICE/spice,SPICE/spice,fgouget/spice