Fix #5052: Guard potentially undefined `e_PAGE` constant

[Deltik]

Motivation and Context

Fixes: https://github.com/e107inc/e107/issues/5052

Description

Guard potentially undefined e_PAGE constant

How Has This Been Tested?

By manually running through the "How to Reproduce" steps in https://github.com/e107inc/e107/issues/5052

Types of Changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Performance enhancement (non-breaking change which improves efficiency)
• [ ] Code cleanup (non-breaking change which makes code smaller or more readable)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation (a change to man pages or other documentation)

Checklist

• [x] My code adheres to the e107 code style standard.
• [x] I have read the contributing document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests pass.

[codeclimate[bot]]

Code Climate has analyzed commit 68b2401b and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Bug Risk	1

The test coverage on the diff in this pull request is 0.0% (80% is the threshold).

This pull request will bring the total coverage in the repository to 34.1% (-0.8% change).

View more on Code Climate.

[CaMer0n]

Thank you. Closed in favor of https://github.com/e107inc/e107/commit/5ff319cd5c55e0a5a90c33af5d713b02037e585d