Handle nil TaskInfo in task.Wait callback (#665)
Handle nil TaskInfo in task.Wait callback (#665)

Property collector returns nil when it cannot find the task, handle
that case in the Error method which gets called by callback. Otherwise
we panic.

Towards https://github.com/vmware/vic/issues/3868
bruceadowns/govmomi,casualjim/govmomi,caglar10ur/govmomi,dougm/govmomi,caglar10ur/govmomi,jrmycanady/govmomi,dougm/govmomi,bruceadowns/govmomi,caglar10ur/govmomi,casualjim/govmomi,jrmycanady/govmomi,vmware/govmomi,dougm/govmomi,bruceadowns/govmomi,casualjim/govmomi,jrmycanady/govmomi,vmware/govmomi,vmware/govmomi