for linux packageName is empty so using appName

Author: lohanidamodar

templates/flutter/lib/client.dart.twig

@@ -90,7 +90,7 @@ class Client {
             cookieJar = new PersistCookieJar(dir:cookieDir.path);
             this.http.interceptors.add(CookieManager(cookieJar));
             PackageInfo packageInfo = await PackageInfo.fromPlatform();
-            addHeader('Origin', 'appwrite-$type://${packageInfo.packageName}');
+            addHeader('Origin', 'appwrite-$type://${packageInfo.packageName ?? packageInfo.appName}');
           }else{
             // if web set httpClientAdapter as BrowserHttpClientAdapter with withCredentials true to make cookies work
             this.http.options.extra['withCredentials'] = true;