upgrade to irc-go v0.4.0

vendor/github.com/ergochat/irc-go/ircmsg/unicode.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2021 Shivaram Lingamneni
+// Released under the MIT License
+
+package ircmsg
+
+import (
+	"unicode/utf8"
+)
+
+// TruncateUTF8Safe truncates a message, respecting UTF8 boundaries. If a message
+// was originally valid UTF8, TruncateUTF8Safe will not make it invalid; instead
+// it will truncate additional bytes as needed, back to the last valid
+// UTF8-encoded codepoint. If a message is not UTF8, TruncateUTF8Safe will truncate
+// at most 3 additional bytes before giving up.
+func TruncateUTF8Safe(message string, byteLimit int) (result string) {
+	if len(message) <= byteLimit {
+		return message
+	}
+	message = message[:byteLimit]
+	for i := 0; i < (utf8.UTFMax - 1); i++ {
+		r, n := utf8.DecodeLastRuneInString(message)
+		if r == utf8.RuneError && n <= 1 {
+			message = message[:len(message)-1]
+		} else {
+			break
+		}
+	}
+	return message
+}