Just wanted to add that this still works with Kodi v19 with one small change. You have to Setup the location with a username and password even though it isn't protected. I'm pretty sure anything works, but I just use the letter "a" for both
To edit a previously working share, long press on the share and select "Edit Source". Then click "Browse" and find the share from the list. It will either be an IP Address or your computer name (For me, it would either be smb:\\192.168.1.1 or smb:\\KAJUN-PC). Long press on this source and select "Edit Network Location". Add something to the username and password fields and press "OK". You should be able to just hit cancel until your back in Videos and have a working source again.
To add a new source:
Adding_video_sources (wiki)
After step 4, we need to add our source to the list, so scroll to the bottom and select "+ Add Network Location".
Next, set the following:
Protocol: SMB
Server name: <ComputerName> or <IP Adress> (mine could be KAJUN-PC or 192.168.1.1
Shared folder: <FolderName> (can be left blank and navigated to after)
Username: <anything>
Password: <anything>
This will add the Share as a source you can select in Step 5. Select your source, navigate to your videos and hit "OK". Continue with Step 6 and your done. It can seem like it freezes/hangs if your library is big, but it'll catch up.