fix(config): add null coalescing fallback in getValueBool before strtolower

Followup to #59646: guard against null reaching strtolower() in both
AppConfig and UserConfig getValueBool(). Also aligns AppConfig with the
(string) cast added in UserConfig by the original PR.

Signed-off-by: skjnldsv <skjnldsv@protonmail.com>

Author: skjnldsv

lib/private/AppConfig.php

@@ -437,7 +437,11 @@ public function getValueFloat(string $app, string $key, float $default = 0, bool
 	 */
 	#[\Override]
 	public function getValueBool(string $app, string $key, bool $default = false, bool $lazy = false): bool {
-		$b = strtolower($this->getTypedValue($app, $key, $default ? 'true' : 'false', $lazy, self::VALUE_BOOL));
+		// The explicit (string) cast guards against a PHP OPcache bug where values passed
+		// by reference across function boundaries can have their type corrupted (e.g. bool
+		// returned as int). Affects PHP 8.x with OPcache enabled; fixed upstream in
+		// https://github.com/php/php-src/pull/21973. Keep until minimum PHP version is bumped.
+		$b = strtolower((string)$this->getTypedValue($app, $key, $default ? 'true' : 'false', $lazy, self::VALUE_BOOL) ?? 'false');
 		return in_array($b, ['1', 'true', 'yes', 'on']);
 	}
 

lib/private/Config/UserConfig.php

@@ -709,7 +709,7 @@ public function getValueBool(
 		// by reference across function boundaries can have their type corrupted (e.g. bool
 		// returned as int). Affects PHP 8.x with OPcache enabled; fixed upstream in
 		// https://github.com/php/php-src/pull/21973. Keep until minimum PHP version is bumped.
-		$b = strtolower((string)$this->getTypedValue($userId, $app, $key, $default ? 'true' : 'false', $lazy, ValueType::BOOL));
+		$b = strtolower((string)$this->getTypedValue($userId, $app, $key, $default ? 'true' : 'false', $lazy, ValueType::BOOL) ?? 'false');
 		return in_array($b, ['1', 'true', 'yes', 'on']);
 	}