PDF Export dosen't work when setting "MAXIMUM CONTENT SIZE" to 0

Steps to reproduce:

1. Access Administer Wiki > Content > PDF Export
2. Set the MAXIMUM CONTENT SIZE (The maximum content size, in kilobytes (KB), that can be included in a single PDF export. Use 0 to disable the limit.) to 0 to disable it

Expected results: The maximum content size is disabled and the user can export large documents.

Actual results:  None of the exports work anymore.

The following message appears when exporting as PDF even a simple page "Failed to export as PDF: RuntimeException: Maximum content size limit exceeded."