Trim existing slashes, before appending new ones

If working dir is "/" normalizeWorkingDir will add double "//" that breaks S3 functionality

Author: exabyssus

src/LfmPath.php

@@ -177,11 +177,11 @@ public function normalizeWorkingDir()
             ?: $this->helper->getRootFolder();
 
         if ($this->is_thumb) {
-            $path .= Lfm::DS . $this->helper->getThumbFolderName();
+            $path = rtrim($path, Lfm::DS) . Lfm::DS . $this->helper->getThumbFolderName();
         }
 
         if ($this->getName()) {
-            $path .= Lfm::DS . $this->getName();
+            $path = rtrim($path, Lfm::DS) . Lfm::DS . $this->getName();
         }
 
         return $path;