better render error text for the Wender body

src/lib.rs

@@ -123,7 +123,7 @@ impl Wender for askama::Result<String> {
     fn wender(self) -> Response {
         let b = self.unwrap_or_else(|e| {
             tracing::error!("got error rendering template: {e}");
-            "".to_string()
+            "could not render template".to_string()
         });
         Body::new(b).into_response()
     }