Use AuthorSignature as a fallback username (telegram) (#1979)

This comes in handy for annoucement type channels where neither the SenderChat or From structs contain name information.

Also Tweak username logic as when using a full name the username field can be " " instead of "".

bridge/telegram/handlers.go

@@ -128,7 +128,9 @@ func (b *Btelegram) handleUsername(rmsg *config.Message, message *tgbotapi.Messa
 			rmsg.Username = message.From.FirstName
 		}
 		if b.GetBool("UseFullName") {
-			rmsg.Username = message.From.FirstName + " " + message.From.LastName
+			if message.From.FirstName != "" && message.From.LastName != "" {
+				rmsg.Username = message.From.FirstName + " " + message.From.LastName
+			}
 		}
 		if rmsg.Username == "" {
 			rmsg.Username = message.From.UserName
@@ -148,7 +150,9 @@ func (b *Btelegram) handleUsername(rmsg *config.Message, message *tgbotapi.Messa
 			rmsg.Username = message.SenderChat.FirstName
 		}
 		if b.GetBool("UseFullName") {
-			rmsg.Username = message.SenderChat.FirstName + " " + message.SenderChat.LastName
+			if message.SenderChat.FirstName != "" && message.SenderChat.LastName != "" {
+				rmsg.Username = message.SenderChat.FirstName + " " + message.SenderChat.LastName
+			}
 		}
 
 		if rmsg.Username == "" || rmsg.Username == "Channel_Bot" {
@@ -164,6 +168,11 @@ func (b *Btelegram) handleUsername(rmsg *config.Message, message *tgbotapi.Messa
 		}
 	}
 
+	// Fallback on author signature (used in "channel" type of chat)
+	if rmsg.Username == "" && message.AuthorSignature != "" {
+		rmsg.Username = message.AuthorSignature
+	}
+
 	// if we really didn't find a username, set it to unknown
 	if rmsg.Username == "" {
 		rmsg.Username = unknownUser