Ensure the output buffer is empty prior to attempting to generate a pdf.

In order to generate a pdf, the output buffer MUST be empty, or else tcpdf shall return an error.

Description

This commit fixes #10695 , and flushes the active output buffer prior to attempting to generate a pdf.

As noted in the bug report, if tcpdf sees the output buffer is not empty, it will fail with a cryptic error.

Motivation and Context

This ensures that we do not subsequently fail the ob_get_contents() checks conducted by tcpdf when generating a pdf output.

How To Test This

This change was tested on our local installation of suiteCRM.

Types of changes

• [X ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• [X ] My code follows the code style of this project found here.
• My change requires a change to the documentation.
• I have read the How to Contribute guidelines.