Welcome bot will not let me add a message to private channels

[DHaussermann]

Seems like the feature of adding a channel level welcome message should work for both public and private channels.
When I try using this feature I see a message saying this is not supported for DM channels. However the channel is not a DM.

Steps:

• Create or open any private channel
• Type /welcomebot set_channel_welcome "I like pickles"
  Observed: welcome messages are not supported for direct channels

[hanzei]

It works exactly like the code dictates it: https://github.com/mattermost/mattermost-plugin-welcomebot/blob/29c0079329652a42c852ade6aa9309359777f22b/server/command.go#L133-L136

[eng-user01]

I was surprised to run into this (why shouldn't it work in a private channel?) and confused by the misleading error message.

[hanzei]

Yes, the code is wrong. Only direct channels should be prohibited, not private ones.

[mickmister]

Reopening since the fix PR has been reverted #109