`toDouble()` can throw exception due to issue in BigInt

[toddobryan]

Try the following:

  BigDecimal bd = BigDecimal.parse("6.6880440087720299389e+806");
  print(bd.toDouble());

I get the following exception:

Unhandled exception:
Invalid argument(s): Exponent must not be negative: -787
#0      _BigIntImpl.pow (dart:core-patch/bigint_patch.dart:1872:7)
#1      BigDecimal.toDouble (package:big_decimal/src/big_decimal.dart:166:43)

It even fails if you change the e+806 to something as small as e+21.

[toddobryan]

OK. BigDecimal.parse("1e2").toDouble() throws the same exception.