Fix bug with percent formats with no integer part

lib/src/intl/number_format.dart

Index: lib/src/intl/number_format.dart
diff --git a/lib/src/intl/number_format.dart b/lib/src/intl/number_format.dart
index 2e23d358e7947d871e761cb063ff613886cc5b42..e9d61c76121a606a6679e36f015b4a9c7e27295d 100644
--- a/lib/src/intl/number_format.dart
+++ b/lib/src/intl/number_format.dart
@@ -310,7 +310,7 @@ class NumberFormat {
     var integerDigits = _integerDigits(integerPart, extraIntegerDigits);
     var digitLength = integerDigits.length;
 
-    if (_hasPrintableIntegerPart(integerPart)) {
+    if (_hasIntegerDigits(integerDigits)) {
       _pad(minimumIntegerDigits - digitLength);
       for (var i = 0; i < digitLength; i++) {
         _addDigit(integerDigits.codeUnitAt(i));
@@ -389,8 +389,8 @@ class NumberFormat {
    * because we have digits left of the decimal point, or because there are
    * a minimum number of printable digits greater than 1.
    */
-  bool _hasPrintableIntegerPart(x) =>
-      x > 0 || minimumIntegerDigits > 0;
+  bool _hasIntegerDigits(String digits) =>
+      digits.isNotEmpty || minimumIntegerDigits > 0;
 
   /** A group of methods that provide support for writing digits and other
    * required characters into [_buffer] easily.