fix: fixed the panic when getting nil chat.

bot.go

@@ -200,7 +200,14 @@ func (bot *Bot) Run() error {
 		u := &Update{
 			Update: &up,
 		}
-		chn, ok := handles[u.FromChat().Type]
+
+		// Sometimes returns nil.
+		fromChat := u.FromChat()
+		if fromChat == nil {
+			continue
+		}
+
+		chn, ok := handles[fromChat.Type]
 		if !ok {
 			continue
 		}