MdeModulePkg/BdsDxe: Fix calling PlatformBootManagerWaitCallback on 0

MdeModulePkg/BdsDxe: Fix calling PlatformBootManagerWaitCallback on 0

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2266

Commit 2de1f611be06ded3a59726a4052a9039be7d459b introduced a regression
whereas platforms that did set PcdPlatformBootTimeOut to 0 are now getting
an unexpected call to PlatformBootManagerWaitCallback().

This patch also ensures that, if PcdPlatformBootTimeOut is 0xFFFF we don't
call PlatformBootManagerWaitCallback() with a zero argument as doing so
would produce an unwarranted jump to full progress completion which is
likely to throw off users.

Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Liming Gao <liming.gao@intel.com>