Describe the bug

When using the Advanced NSRDB Dialog in the 2020.11.29 release, the advanced nsrdb download widget resets the library folder list in the UI if you write the downloaded files to a folder not already in the library

To Reproduce

Steps to reproduce the behavior:

1. Go to PV case in SAM 2020.11.29
2. Check 'Advanced download' on Location and Resource page
3. Click 'Download and add to library'
4. Select any weather file
5. Browse to a folder location not already in the library_folder_list
6. Press Ok to download weather file, see library folder list rewrite

Expected behavior

New folder is appended to the library folder list without losing any other folders besides ../SAM Downloaded Weather Files

Screenshots

In invoke.cpp:

Additional context

Found when working on wave resource download widget