Avoid panic when spec file is missing sections under Resources
Avoid panic when spec file is missing sections under Resources

Check pointers against nil before dereferencing them. Skip any sections
that are nil, since that's equivalent to having no values defined for
those sections.

Signed-off-by: Aaron Lehmann <8ecfc6017a87905413dcd7d63696a2a4c351b604@docker.com>

mikebrow/containerd,kunalkushwaha/containerd,crosbymichael/containerd,miaoyq/containerd,containerd/containerd,AkihiroSuda/containerd,containerd/containerd,thaJeztah/containerd,estesp/containerd,xiekeyang/containerd,estesp/containerd,Wolphin-project/containerd,miaoyq/containerd,rajasec/containerd,crosbymichael/containerd,dmcgowan/containerd,yuexiao-wang/containerd,dmcgowan/containerd,chanezon/containerd,amitkris/containerd,thaJeztah/containerd,vdemeester/containerd,kunalkushwaha/containerd,vdemeester/containerd,lichao-mobanche/containerd,mikebrow/containerd,docker/containerd,hqhq/containerd,amitkris/containerd