fix harmless typo in InputsChannel::handle_modifiers
fix harmless typo in InputsChannel::handle_modifiers

InputsChannel::handle_modifiers converts _modifiers which is a
bitflag of SPICE_KEYBOARD_MODIFIER_FLAGS_* to a Platform::*_MODIFIER
bitflag, which is what Platform::set_keyboard_lock_modifiers expects.
However, it's called with _modifiers, and the bitflag that this
function computes is never used. Pass the computed bitflag to
::set_keyboard_lock_modifiers since _modifiers format is meaningless
for ::set_keyboard_lock_modifiers.
This bug was harmless because the two different set of modifier
flags actually use the same values, so _modifiers and modifiers could
be used interchangeably. However it's more future-proof to use the
right format here.

alon/spice-server,ya-mouse/spice,dezelin/spice,alon/spice-server,Fantu/spice,elmarco/spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,mathslinux/spice,dezelin/spice,SPICE/spice,dezelin/spice,ya-mouse/spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,ya-mouse/spice,Fantu/spice,dezelin/spice,fgouget/spice,elmarco/spice,alon/spice-server,elmarco/spice,alon/spice-server,dezelin/spice,freedesktop-unofficial-mirror/spice__spice,mathslinux/spice,SPICE/spice,fgouget/spice,Fantu/spice,mathslinux/spice,mathslinux/spice,fgouget/spice,mathslinux/spice,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,alon/spice-server,Fantu/spice,freedesktop-unofficial-mirror/spice__spice