Make resending `OutPending` messages possible

[iequidoo]

Otherwise it's complicated to implement bots that resend messages when a new member joins the group as noted by @adbenitez:

only situation it will not work because I didn't cover it for simplicity is when two people join about the same time and then the bot can't re-send because the message is already pending state, ideally you would track a "needs resend" flag and then try resending when possible

It should be possible to schedule one more sending of the message, no need even to cancel the existing one.