Curvepoints fix causing plugin to be disabled

[TheWitness]

This is an additional fix to #219 where the count function was failing due to the curvepoints variable not being a countable object, in other words, not being an array. This error would be ignored in earlier versions of PHP.

[Copilot]

Pull request overview

This PR addresses a PHP 8+ compatibility issue where count() was being called on a non-countable curvepoints value, which could trigger a fatal TypeError and cause Cacti to disable the weathermap plugin during CMDPHP execution.

Changes:

• Initialize WeatherMapLink::$curvepoints as an empty array to ensure it is always countable.
• Replace count()/sizeof() calls with Cacti-safe helpers (cacti_count(), cacti_sizeof()) in WeatherMapLink where non-arrays could otherwise trigger fatal errors.
• Minor formatting/cleanup in curve calculation helpers (calc_curve, calc_straight) for consistency (no behavioral change intended).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/WeatherMapLink.class.php	Ensures curvepoints/vialist are handled as countable structures and uses Cacti-safe counting helpers to prevent PHP 8+ fatal errors.
lib/WeatherMap.functions.php	Minor formatting/return-style cleanup in curve helper functions; no functional logic changes.