Redirected download doesn't validate SHA of artifact

[andsel]

After #105 if an URL is redirected then the SHA validation breaks because try to compare with empty string.

% bundle exec rake vendor
Downloading https://github.com/collectd/collectd/archive/refs/tags/collectd-5.4.2.tar.gz
Follow redirect to: https://codeload.github.com/collectd/collectd/tar.gz/refs/tags/collectd-5.4.2
rake aborted!
SHA1 does not match (expected '69d00bf0589adc53c65e48ec18fe636b3efe2306' but got '')
/Users/andrea/.rvm/gems/jruby-9.4.2.0/gems/logstash-devutils-2.6.1-java/lib/logstash/devutils/rake/vendor.rake:20:in `fetch'
/Users/andrea/.rvm/gems/jruby-9.4.2.0/gems/logstash-devutils-2.6.1-java/lib/logstash/devutils/rake/vendor.rake:31:in `block in file_fetch'
org/jruby/ext/monitor/Monitor.java:82:in `synchronize'
/Users/andrea/.rvm/gems/jruby-9.4.2.0/gems/logstash-devutils-2.6.1-java/lib/logstash/devutils/rake/vendor.rake:36:in `file_fetch'
/Users/andrea/.rvm/gems/jruby-9.4.2.0/gems/logstash-devutils-2.6.1-java/lib/logstash/devutils/rake/vendor.rake:172:in `block in <main>'
/Users/andrea/.rvm/gems/jruby-9.4.2.0/gems/logstash-devutils-2.6.1-java/lib/logstash/devutils/rake/vendor.rake:171:in `block in <main>'
org/jruby/ext/monitor/Monitor.java:82:in `synchronize'
org/jruby/ext/monitor/Monitor.java:82:in `synchronize'
/Users/andrea/.rvm/gems/jruby-9.4.2.0/gems/rake-13.1.0/exe/rake:27:in `<main>'
/Users/andrea/.rvm/gems/jruby-9.4.2.0/bin/jruby_executable_hooks:22:in `<main>'
Tasks: TOP => vendor/collectd-5.4.2.tar.gz
(See full trace by running task with --trace)

The problem is

SHA1 does not match (expected '69d00bf0589adc53c65e48ec18fe636b3efe2306' but got '')