fix: make access denied message a bit clearer

Signed-off-by: Robin Appelman <robin@icewind.nl>

lib/Operation.php

@@ -103,7 +103,7 @@ public function checkFileAccess(IStorage $storage, string $path, bool $isDir = f
 			$e = new \RuntimeException('Access denied for path ' . $path . ' that is ' . ($isDir ? '' : 'not ') . 'a directory and matches rules: ' . json_encode($match));
 			$this->logger->debug($e->getMessage(), ['exception' => $e]);
 			// All Checks of one operation matched: prevent access
-			throw new ForbiddenException('Access denied', false);
+			throw new ForbiddenException('Access denied by access control', false);
 		}
 	}