Improve Debug formatting of the thread name.

src/thread.rs

@@ -132,13 +132,9 @@ fn check_terminated(&mut self) -> bool {
 impl<'mir, 'tcx> std::fmt::Debug for Thread<'mir, 'tcx> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         if let Some(ref name) = self.thread_name {
-            if let Ok(name_str) = std::str::from_utf8(name) {
-                write!(f, "{}", name_str)?;
-            } else {
-                write!(f, "<invalid thread name>")?;
-            }
+            write!(f, "{}", String::from_utf8_lossy(name))?;
         } else {
-            write!(f, "unnamed")?;
+            write!(f, "<unnamed>")?;
         }
         write!(f, "({:?}, {:?})", self.state, self.join_status)
     }