qemu: Resolve Coverity UNINIT
    
    For some reason, commit id '72b4151f' triggered a Coverity uninitialized
    'reply' variable check when referenced within the for loop.
    
    It seems Coverity doesn't know that flags will have to be either AFFECT_LIVE
    or AFFECT_CONFIG after the virDomainLiveConfigHelperMethod call.
    
    By adding a "sa_assert()" to confirm that fact, Coverity is happy again.