KVM: LAPIC: ignore pending timers if LVTT is disabled

Only use the APIC pending timers count to break out of HLT emulation if
the timer vector is enabled.

Certain configurations of Windows simply mask out the vector without
disabling the timer.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>