lib: Only render listing caption if not empty
lib: Only render listing caption if not empty

If title or actions properties are not provided for Listing component,
the <caption> tag is not rendered to save space.

Reviewed-by: Dominik Perpeet <dperpeet@redhat.com>

fixup by Dominik Perpeet: Code style

harishanand95/cockpit,cockpit-project/cockpit,xhad/cockpit,mvollmer/cockpit,cockpituous/cockpit,SotolitoLabs/cockpit,martinpitt/cockpit,harishanand95/cockpit,dperpeet/cockpit,moraleslazaro/cockpit,michalskrivanek/cockpit,larsu/cockpit,michalskrivanek/cockpit,Scribery/cockpit,martinpitt/cockpit,mareklibra/cockpit,moraleslazaro/cockpit,larskarlitski/cockpit,cockpit-project/cockpit,cockpituous/cockpit,larskarlitski/cockpit,larsu/cockpit,stefwalter/cockpit,Scribery/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,mvollmer/cockpit,xhad/cockpit,petervo/cockpit,garrett/cockpit,andreasn/cockpit,xhad/cockpit,SotolitoLabs/cockpit,martinpitt/cockpit,SotolitoLabs/cockpit,petervo/cockpit,larsu/cockpit,Scribery/cockpit,mvollmer/cockpit,stefwalter/cockpit,petervo/cockpit,deryni/cockpit,petervo/cockpit,harishanand95/cockpit,martinpitt/cockpit,larskarlitski/cockpit,cockpituous/cockpit,dperpeet/cockpit,stefwalter/cockpit,michalskrivanek/cockpit,andreasn/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpituous/cockpit,andreasn/cockpit,larskarlitski/cockpit,dperpeet/cockpit,deryni/cockpit,deryni/cockpit,michalskrivanek/cockpit,harishanand95/cockpit,xhad/cockpit,mareklibra/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,petervo/cockpit,andreasn/cockpit,dperpeet/cockpit,petervo/cockpit,deryni/cockpit,Scribery/cockpit,michalskrivanek/cockpit,mareklibra/cockpit,dperpeet/cockpit,deryni/cockpit,Scribery/cockpit,harishanand95/cockpit,xhad/cockpit,harishanand95/cockpit,SotolitoLabs/cockpit,garrett/cockpit,dperpeet/cockpit,michalskrivanek/cockpit,xhad/cockpit,deryni/cockpit,stefwalter/cockpit,larsu/cockpit,larskarlitski/cockpit,garrett/cockpit,larsu/cockpit,stefwalter/cockpit,andreasn/cockpit,larskarlitski/cockpit,cockpituous/cockpit,Scribery/cockpit,martinpitt/cockpit,mareklibra/cockpit,michalskrivanek/cockpit,mareklibra/cockpit,stefwalter/cockpit,mvollmer/cockpit,xhad/cockpit,SotolitoLabs/cockpit,mvollmer/cockpit,dperpeet/cockpit,moraleslazaro/cockpit,garrett/cockpit,mareklibra/cockpit,cockpituous/cockpit,garrett/cockpit,larsu/cockpit,deryni/cockpit,SotolitoLabs/cockpit,Scribery/cockpit,larskarlitski/cockpit,moraleslazaro/cockpit,andreasn/cockpit,moraleslazaro/cockpit,stefwalter/cockpit,petervo/cockpit,harishanand95/cockpit,andreasn/cockpit