Fix file sharing via public link for one particular file.

Fix OC_Files::get() to not return the first character of the filename
if only one file is requested.

lib/files.php

@@ -50,7 +50,7 @@ public static function get($dir, $files, $only_header = false) {
 			$xsendfile = true;
 		}
 
-		if (count($files) == 1) {
+		if (is_array($files) && count($files) == 1) {
 			$files = $files[0];
 		}