Fix regression introduced when inlining "Required" (#2005)

If the description is not set in the object definition, Hugo generates a weird string after "Required": `%!s(<nil>)`.

To avoid that, we default the description to an empty string when it is not set.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

changelogs/internal/newsfragments/2005.clarification

@@ -0,0 +1 @@
+Enforce consistent vertical spacing between paragraphs in endpoint definitions.

layouts/partials/openapi/render-object-table.html

@@ -313,7 +313,7 @@ resolve-additional-types.)
           Prepend "Required:" to make it part of the first paragraph of the
           description.
         */}}
-        {{- $description = printf "<strong>Required: </strong>%s" $description -}}
+        {{- $description = printf "<strong>Required: </strong>%s" (default "" $description) -}}
     {{ end -}}
     {{/*
       Force the rendering as a block so the description is always inside a