Fix possible segfault in config reload
Fix possible segfault in config reload

This commit fixes two possible crashes in the `*Daemon` bound method
`reloadMaxConcurrentDownloadsAndUploads()`.

The first fixed issue is when `daemon.imageService` is `nil`. The second
panic can occur if the provided `*config.Config` is incomplete and the
fields `conf.MaxConcurrentDownloads` or `conf.MaxConcurrentUploads` are
`nil`.

Signed-off-by: Sascha Grunert <70ab469ddb2ac3e35f32ed7c2fd1cca514b2e879@suse.com>

rancher/docker,mikebrow/docker,maxamillion/docker,mikebrow/docker,Ramzec/docker,kojiromike/docker,trebonian/docker,flavio/docker,AkihiroSuda/docker,justincormack/docker,docker/docker,Ramzec/docker,trebonian/docker,tmp6154/docker,mikebrow/docker,konstruktoid/docker-1,jlhawn/docker,maxamillion/docker,paralin/docker,rremer/moby,gnailuy/docker,flavio/docker,estesp/docker,trebonian/docker,ibuildthecloud/docker,tmp6154/docker,cpuguy83/docker,jameszhan/docker,rancher/docker,kolyshkin/moby,SvenDowideit/docker,paralin/docker,thaJeztah/docker,scotttlin/docker,SvenDowideit/docker,jimjag/docker,crosbymichael/docker,bearstech/moby,flavio/docker,rremer/moby,mahak/docker,scotttlin/docker,dims/docker,KarthikNayak/docker,moby/moby,Mokolea/docker,maxamillion/docker,jimjag/docker,jameszhan/docker,cpuguy83/docker,justincormack/docker,jvanz/docker,tmp6154/docker,Mokolea/docker,estesp/docker,unclejack/docker,ibuildthecloud/docker,gnailuy/docker,thaJeztah/docker,konstruktoid/docker-1,Mokolea/docker,rremer/moby,moby/moby,x1022as/docker,nawawi/docker,Ramzec/docker,konstruktoid/docker-1,kojiromike/docker,yosifkit/docker,AkihiroSuda/docker,pradipd/moby,KarthikNayak/docker,mahak/docker,moul/docker,jwhonce/docker,dims/docker,konstruktoid/docker-upstream,jthelin/docker,ibuildthecloud/docker,vdemeester/docker,docker/docker,jvanz/docker,yongtang/docker,unclejack/docker,jthelin/docker,paralin/docker,scotttlin/docker,x1022as/docker,kolyshkin/moby,pradipd/moby,jameszhan/docker,yosifkit/docker,yosifkit/docker,thaJeztah/docker,estesp/docker,kojiromike/docker,nawawi/docker,jlhawn/docker,moby/moby,mahak/docker,bearstech/moby,jimjag/docker,nalind/docker,moul/docker,trebonian/docker,AkihiroSuda/docker,gnailuy/docker,AkihiroSuda/docker,yosifkit/docker,moul/docker,kolyshkin/moby,jimjag/docker,justincormack/docker,vdemeester/docker,ibuildthecloud/docker,konstruktoid/docker-upstream,vdemeester/docker,bearstech/moby,dims/docker,djs55/docker,cpuguy83/docker,djs55/docker,pradipd/moby,nalind/docker,Mokolea/docker,crosbymichael/docker,mahak/docker,paralin/docker,SvenDowideit/docker,jwhonce/docker,moby/moby,cpuguy83/docker,crosbymichael/docker,nawawi/docker,konstruktoid/docker-upstream,jvanz/docker,yongtang/docker,flavio/docker,docker/docker,x1022as/docker,yongtang/docker,konstruktoid/docker-upstream,nalind/docker,KarthikNayak/docker,thaJeztah/docker,ibuildthecloud/docker,jwhonce/docker,gnailuy/docker,bearstech/moby,moul/docker,jlhawn/docker,Ramzec/docker,unclejack/docker,nalind/docker,djs55/docker,rancher/docker,nawawi/docker