bignum.c: rb_int_parse_cstr handle `0` strings

[Bug #19390]

We shouldn't check the string length when skipping zeros, as the
string might only contains zero characters, resulting in an empty string.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/ruby/test_time.rb b/test/ruby/test_time.rb
index 38c1af6901..2bf6056a49 100644
--- a/test/ruby/test_time.rb
+++ b/test/ruby/test_time.rb
@@ -1426,4 +1426,8 @@ class TestTime < Test::Unit::TestCase
       t.deconstruct_keys(%i[year month sec nonexistent])
     )
   end
+
+  def test_parse_zero_bigint
+    assert_equal 0, Time.new("2020-10-28T16:48:07.000Z").nsec, '[Bug #19390]'
+  end
 end