Issue #3445072 by longwave, Anybody: Improve "The libraries to include are...

Issue #3445072 by longwave, Anybody: Improve "The libraries to include are encoded incorrectly" check and message

(cherry picked from commit 803c9429)

core/modules/system/src/Controller/AssetControllerBase.php

@@ -162,10 +162,11 @@ public function deliver(Request $request, string $file_name) {
     $attached_assets = new AttachedAssets();
     $include_libraries = explode(',', UrlHelper::uncompressQueryParameter($request->query->get('include')));
 
+    // Check that library names are in the correct format.
     $validate = function ($libraries_to_check) {
       foreach ($libraries_to_check as $library) {
-        if (substr_count($library, '/') !== 1) {
-          throw new BadRequestHttpException('The libraries to include are encoded incorrectly.');
+        if (substr_count($library, '/') === 0) {
+          throw new BadRequestHttpException(sprintf('The "%s" library name must include at least one slash.', $library));
         }
       }
     };