kvm: nVMX: Set nested_run_pending in vmx_set_nested_state after checks complete

nested_run_pending=1 implies we have successfully entered guest mode.
Move setting from external state in vmx_set_nested_state() until after
all other checks are complete.

Based on a patch by Aaron Lewis.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>