Force SSL on sub folder
For better practice, you should never use ".htaccess" file. Especially your problem can be easily solved by modify Apache configure file.

You should be able to find an Apache configure file somewhere in your /etc folder. 
On my server its /etc/httpd/conf/httpd.conf.

Then just find the code 

&lt;VirtualHost *:80&gt;
   ... your server setting
   ServerName your-server-address.com
   # add the following line
   Redirect permanent / https://your-server-address.com/
&lt;/VirtualHost&gt;


Don't forget to restart your server after you done the change.
This will redirect any traffic trying to visit your site with none ssl to ssl, regardless your folder structure.