rune: Do not trace return value (causes panic on Result:Err) (#748)

Do not trace return value (causes panic on Result:Err)

Instead attempt to print *something*

crates/rune/src/runtime/value.rs

@@ -2137,7 +2137,15 @@ impl fmt::Debug for Value {
         let mut o = Formatter::new();
 
         if self.string_debug(&mut o).is_err() {
-            return Err(fmt::Error);
+            match self.type_info() {
+                Ok(type_info) => {
+                    write!(f, "<{} object at {:p}>", type_info, self)?;
+                }
+                Err(e) => {
+                    write!(f, "<unknown object at {:p}: {}>", self, e)?;
+                }
+            }
+            return Ok(());
         }
 
         f.write_str(o.as_str())?;

crates/rune/src/runtime/vm.rs

@@ -2239,7 +2239,7 @@ impl Vm {
     }
 
     #[inline]
-    #[tracing::instrument(skip(self))]
+    #[tracing::instrument(skip(self, return_value))]
     fn op_return_internal(&mut self, return_value: Value) -> VmResult<Option<Output>> {
         let (exit, out) = vm_try!(self.pop_call_frame());