Fix FormCalc Round overflowing to infinity for large values (#4508)

Found while testing crates/js/src/formcalc.rs:2114-2119

Co-authored-by: Claude Haiku 5.5 <noreply@anthropic.com>

crates/js/src/formcalc.rs

@@ -2115,7 +2115,8 @@ impl Interp<'_> {
                 let a = self.arg_num(args, 0)?;
                 let places = if args.len() > 1 { self.arg_num(args, 1)?.clamp(0.0, 12.0) as i32 } else { 0 };
                 let k = 10f64.powi(places);
-                Val::Num((a * k).round() / k)
+                let scaled = a * k;
+                if scaled.is_finite() { Val::Num(scaled.round() / k) } else { Val::Num(a) }
             }
             "count" => {
                 // Non-null values and objects: an empty field doesn't count, a subform does.

crates/js/src/tests.rs

@@ -1009,6 +1009,12 @@ mod formcalc {
         assert_eq!(calc(r#"Format("9.99", 2.344)"#), "2.34");
     }
 
+    #[test]
+    fn round_keeps_huge_values_finite() {
+        assert_eq!(calc("Round(1e300, 12) == 1e300"), "1");
+        assert_eq!(calc("Round(1.2345, 2)"), "1.23");
+    }
+
     #[test]
     fn built_in_functions_cover_the_common_set() {
         assert_eq!(calc("Abs(-2.5)"), "2.5");