Don't show empty documentation labels in completions menu (#3632)

This PR fixes an issue where we would sometimes have extra blank lines
in the completions menu.

This was due to some items including documentation labels that were
empty strings.

Release Notes:

- N/A

crates/editor2/src/editor.rs

@@ -1250,6 +1250,7 @@ impl CompletionsMenu {
                         let documentation_label =
                             if let Some(Documentation::SingleLine(text)) = documentation {
                                 Some(SharedString::from(text.clone()))
+                                    .filter(|text| !text.trim().is_empty())
                             } else {
                                 None
                             };