Reactions Broken on Channels - Fix Attached

### 🐞 Bug Report

Telegram Bot errors out when doing a handleGetUpdates ("Call to a member function getChat() on null") after a user reacts to a channel post. Here's the fix.

In DB::insertMessageReactionCount, this line referencing $message_reaction should be this:

`
if ($chat = $message_reaction_count->getChat()) {
`
