skip printing empty rows in tablePrinter

[mwennrich]

Nicer output when using conditionals in template output.

Before:

$ cloudctl cluster ls -o template --template '{{ if eq .Networking.Type "cilium" }}{{ .Name }}{{end}}'






cilium

With this PR:

$ cloudctl ls -o template --template '{{ if eq .Networking.Type "cilium" }}{{ .Name }}{{end}}'
cilium

[Gerrit91]

Tried to carry this over to the metal-lib because in the end I would like to use the printers from this library also for cloudctl.