When doing `docker service inspect --pretty` on services without
`TaskTemplate.Resources` or `TaskTemplate.Resources.Limits`, the command
fails. This is due to a missing check on ResourceLimitPids().
This bug has been introduced by 395a6d560d
and produces following error message:
```
Template parsing error: template: :139:10: executing "" at <.ResourceLimitPids>: error calling ResourceLimitPids: runtime error: invalid memory address or nil pointer dereference
```
Signed-off-by: Albin Kerouanton <albin@akerouanton.name>
21da11c5fd