fix(files_external): list root when using SMB case-insensitive option

Signed-off-by: Benjamin Gaussorgues <benjamin.gaussorgues@nextcloud.com>

apps/files_external/lib/Lib/Storage/SMB.php

@@ -683,7 +683,8 @@ class SMB extends Common implements INotifyStorage {
 
 	public function file_exists($path) {
 		try {
-			if ($this->caseSensitive === false) {
+			// Case sensitive filesystem doesn't matter for root directory
+			if ($this->caseSensitive === false && $path !== '') {
 				$filename = basename($path);
 				$siblings = $this->getDirectoryContent(dirname($this->buildPath($path)));
 				foreach ($siblings as $sibling) {