Do not send empty messages

src/groups/calls/events.rs

@@ -111,6 +111,10 @@ impl OnMessageHandler<State, Extras> for CallMessageHandler {
             return Ok(());
         }
 
+        if event.content.is_empty() {
+            return Ok(());
+        }
+
         let Some(guild_id) = event.guild_id else {
             return Ok(());
         };