try fix GBK txt preview

disk/Onedrive.php

@@ -100,11 +100,23 @@ class Onedrive {
                     }
                 }
                 if (isset($files['file'])) {
-                    if (in_array(splitlast($files['name'],'.')[1], $exts['txt'])) {
-                        if (!(isset($files['content'])&&$files['content']['stat']==200)) {
-                            $content1 = curl('GET', $files[$this->DownurlStrName]);
-                            $files['content'] = $content1;
-                            savecache('path_' . $path, $files, $this->disktag);
+                    if (in_array(strtolower(splitlast($files['name'],'.')[1]), $exts['txt'])) {
+                        if ($files['size']<1024*1024) {
+                            if (!(isset($files['content'])&&$files['content']['stat']==200)) {
+                                $content1 = curl('GET', $files[$this->DownurlStrName]);
+                                $tmp = null;
+                                $tmp = json_decode(json_encode($content1), true);
+                                if ($tmp['body']===null) {
+                                    $tmp['body'] = iconv("GBK", 'UTF-8//TRANSLIT', $content1['body']);
+                                    $tmp = json_decode(json_encode($tmp), true);
+                                    if ($tmp['body']!==null) $content1['body'] = $tmp['body'];
+                                }
+                                $files['content'] = $content1;
+                                savecache('path_' . $path, $files, $this->disktag);
+                            }
+                        } else {
+                            $files['content']['stat'] = 202;
+                            $files['content']['body'] = 'File too large.';
                         }
                     }
                 }