feat: stabilize OpenSim interactions and landmarks

tools/codegen/src/lib.rs

@@ -1743,10 +1743,17 @@ fn append_packet_impls(body: &mut String, packets: &[&PacketDefinition]) {
                     );
                 }
                 BlockRepetition::Variable => {
-                    let _ = writeln!(
-                        body,
-                        "        let {field_name}_count = usize::from(reader.read_u8()?);"
-                    );
+                    if packet.name == "ImprovedInstantMessage" && block.name == "MetaData" {
+                        let _ = writeln!(
+                            body,
+                            "        let {field_name}_count = if reader.is_empty() {{ 0 }} else {{ usize::from(reader.read_u8()?) }};"
+                        );
+                    } else {
+                        let _ = writeln!(
+                            body,
+                            "        let {field_name}_count = usize::from(reader.read_u8()?);"
+                        );
+                    }
                     let _ = writeln!(body, "        let mut {field_name} = Vec::new();");
                     let _ = writeln!(
                         body,