chore: fix emoji token rendering in HTML messages (#2913)

lib/pages/chat/chat.dart

@@ -1486,6 +1486,16 @@ class ChatController extends State<ChatPageWithRoom>
   void typeEmoji(Emoji? emoji) {
     if (emoji == null) return;
     final text = sendController.text;
+
+    // #Pangea
+    if (!sendController.selection.isValid) {
+      sendController.value = TextEditingValue(
+        text: text,
+        selection: TextSelection.collapsed(offset: text.length),
+      );
+    }
+    // Pangea#
+
     final selection = sendController.selection;
     final newText = sendController.text.isEmpty
         ? emoji.emoji

lib/pages/chat/events/html_message.dart

@@ -193,8 +193,13 @@ class HtmlMessage extends StatelessWidget {
       if (tokenIndex == -1) continue;
 
       final int tokenLength = tokenText.characters.length;
-      final before = result[substringIndex].substring(0, tokenIndex);
-      final after = result[substringIndex].substring(tokenIndex + tokenLength);
+      final before =
+          result[substringIndex].characters.take(tokenIndex).toString();
+      final after = result[substringIndex]
+          .characters
+          .skip(tokenIndex + tokenLength)
+          .toString();
+
       result.replaceRange(substringIndex, substringIndex + 1, [
         if (before.isNotEmpty) before,
         '<token offset="${token.text.offset}" length="${token.text.length}">$tokenText</token>',