Detect zero receiver of modInverse (may not converge and time out

runtime/lib/bigint.dart

Index: runtime/lib/bigint.dart
diff --git a/runtime/lib/bigint.dart b/runtime/lib/bigint.dart
index 60b42454946acfb08790da4bd7c2fb8c23c8ee11..27c27fa7157c0d374036dc8206613aa0b030048f 100644
--- a/runtime/lib/bigint.dart
+++ b/runtime/lib/bigint.dart
@@ -1542,6 +1542,7 @@ class _Bigint extends _IntegerImplementation implements int {
   int modInverse(int m) {
     if (m is! int) throw new ArgumentError(m);
     if (m <= 0) throw new RangeError(m);
+    if (_used == 0) return 0;
     m = m._toBigint();
     // TODO(regis): Implement modInverse for an even modulus.
     if (m.isEven) throw new UnimplementedError();