Redmine

The application does not respond if we try to export issues to PDF with too many columns (more than 60).

How to reproduce this bug:
1. Create many issue custom fields
You can use this command in the console: (1..60).each { |i| CustomField.new(IssueCustomField.last.attributes.merge!({id:nil,name:"test-#{i}", is_for_all: true})).save }
2. Go to /issues page
3. Choose to display every columns and apply the filter
4. Try to export to PDF

This bug seems to come from the RBPDF Gem. An infinite loop may appear in the "Write" method here:
https://github.com/naitoh/rbpdf/blob/0eff3fdae5a17ec111b63e3825b358a6b34c3f56/lib/rbpdf.rb#L4510
This infinite loop could overload the server and affect website availability.