fix: do not split TextMetrics if theres nothing to split

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "fontkit"
-version = "0.6.0-beta.2"
+version = "0.6.0-beta.3"
 edition = "2021"
 authors = ["Zimon Dai <[email protected]>"]
 description = "A simple library for font loading and indexing"

src/metrics/compose.rs

@@ -563,10 +563,14 @@ impl TextMetrics {
  drop(positions);
  // Split here, create a new span
  let mut new_metrics = self.clone();
- new_metrics.positions = {
- let mut p = self.positions.write().unwrap();
- Arc::new(RwLock::new(p.split_off(real_index)))
- };
+ if real_index == 0 {
+ new_metrics.positions = Arc::new(RwLock::new(vec![]));
+ } else {
+ new_metrics.positions = {
+ let mut p = self.positions.write().unwrap();
+ Arc::new(RwLock::new(p.split_off(real_index)))
+ };
+ }
  new_metrics
  }
 }