fix: prevent preg_replace null from truncating files to 0 bytes

preg_replace returns null on error. Without a null check, the result
was written to files as empty content, destroying all XML manifests
during the release pipeline.

Added null guards to all file_put_contents calls after preg_replace
in version_set_platform.php, version_check.php, and version_bump.php.

Authored-by: Moko Consulting
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cli/version_set_platform.php

@@ -152,7 +152,7 @@ if (in_array($platform, ['waas-component', 'joomla'], true)) {
             "<version>{$version}</version>",
             $content
         );
-        if ($updated !== $content) {
+        if ($updated !== null && $updated !== $content) {
             file_put_contents($file, $updated);
             $relPath = str_replace($root . '/', '', $file);
             echo "Joomla: {$relPath} → {$version}\n";