godot-rust#810 Docs comments do not show up if only some of the class…

… members/methods are documented

- Document `block_docstring_or_empty` function

godot-core/src/docs.rs

@@ -46,6 +46,9 @@ struct DocPieces {
     virtual_methods: Option<&'static str>,
 }
 
+#[doc(hidden)]
+/// Generates documentation for given block if there is anything to document
+/// Returns empty string otherwise
 fn block_docstring_or_empty(block: Option<&'static str>, tag: &'static str) -> String {
     match block {
         Some(s) => format!("<{tag}>{s}</{tag}>"),