Fix #1554: strip prefix before checking directory existence.

Author: frankdejonge

src/WebDAV/WebDAVAdapter.php

@@ -221,7 +221,7 @@ public function createDirectory(string $path, Config $config): void
             $directoryPath = implode('/', $directoryParts);
             $location = $this->encodePath($directoryPath);
 
-            if ($this->directoryExists($directoryPath)) {
+            if ($this->directoryExists($this->prefixer->stripDirectoryPrefix($directoryPath))) {
                 continue;
             }