fix(files_external): boolean comparison of array

To check if there are no missing required dependencies we need to check
if the required dependencies are **empty** because `!array` is still
true.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

apps/files_external/lib/Lib/DependencyTrait.php

@@ -26,7 +26,7 @@ trait DependencyTrait {
 	 *
 	 * @return MissingDependency[] Unsatisfied required dependencies
 	 */
-	public function checkRequiredDependencies() {
+	public function checkRequiredDependencies(): array {
 		return array_filter(
 			$this->checkDependencies(),
 			fn (MissingDependency $dependency) => !$dependency->isOptional()

apps/files_external/lib/Service/BackendService.php

@@ -178,7 +178,7 @@ class BackendService {
 	 * @return Backend[]
 	 */
 	public function getAvailableBackends() {
-		return array_filter($this->getBackends(), fn (Backend $backend) => !$backend->checkRequiredDependencies());
+		return array_filter($this->getBackends(), fn (Backend $backend) => empty($backend->checkRequiredDependencies()));
 	}
 
 	/**