prevent implicit hydration when setting file permissions on shortcuts

we were using specialized API to set the file permissions on the windows
shortcut and later falling back to the generic code path due to the
mising return

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

src/common/filesystembase.cpp

@@ -131,6 +131,7 @@ void FileSystem::setFileReadOnly(const QString &filename, bool readonly)
         {
             qCWarning(lcFileSystem()) << filename << (readonly ? "readonly" : "read write") << e.what();
         }
+        return;
     }
 #endif
     QFile file(filename);