DuetPkg-PciBusNoEnumerationDxe: Fix stack overflow

DuetPkg-PciBusNoEnumerationDxe: Fix stack overflow

When a PCI bridge is not enabled, the secondary bus may still be zero.
This causes an infinite recursive call to enumerate bus 0 which results
in a stack overflow.  The easy fix is to skip the recursive bus
enumeration for bridges which do not have the secondary bus initialized.

TEST=Build and run CorebootPayloadPkg on Quark/Galileo Gen2

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>