prevent panic with format command (#7522)

Related: #7211.

Prevents numeric underflow in span.

Co-authored-by: sholderbach <sholderbach@users.noreply.github.com>

crates/nu-command/tests/commands/format.rs

@@ -42,6 +42,19 @@ fn can_use_variables() {
     assert_eq!(actual.out, "nu is a new type of shell");
 }
 
+#[test]
+fn error_unmatched_brace() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+        open cargo_sample.toml
+            | format "{$it.package.name"
+        "#
+    ));
+
+    assert!(actual.err.contains("unmatched curly brace"));
+}
+
 #[test]
 fn format_filesize_works() {
     Playground::setup("format_filesize_test_1", |dirs, sandbox| {