fix(app-store): Ensure the groups property is always an array

If the value was a string, like a single group, then `json_decode` will also yield only a string.
So in this case we ensure the property is always an array with that value.

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

apps/settings/lib/Controller/AppSettingsController.php

@@ -306,6 +306,10 @@ public function listApps(): JSONResponse {
 			$groups = [];
 			if (is_string($appData['groups'])) {
 				$groups = json_decode($appData['groups']);
+				// ensure 'groups' is an array
+				if (!is_array($groups)) {
+					$groups = [$groups];
+				}
 			}
 			$appData['groups'] = $groups;
 			$appData['canUnInstall'] = !$appData['active'] && $appData['removable'];