Add 'empty' placeholder to prevent automatic text appending in prompts. See #345 and #339

_locales/en/messages.json

@@ -1099,6 +1099,10 @@
     "message": "Default language as defined in ThunderAI options.",
     "description": ""
   },
+  "empty": {
+    "message": "This placeholder doesn't add any text, but it prevents the email body from being automatically appended at the end of the prompt.",
+    "description": ""
+  },
   "prefs_OptionText_spamfilter": {
     "message": "Automatic Spam Filter",
     "description": ""

js/mzta-placeholders.js

@@ -175,6 +175,13 @@ const defaultPlaceholders = [
         type: 0,
         is_default: "1",
     },
+    {
+        id: 'empty',
+        name: "__MSG_placeholder_empty__",
+        default_value: "",
+        type: 0,
+        is_default: "1",
+    },
 ];
 
 
@@ -358,6 +365,9 @@ export const placeholdersUtils = {
                     let prefs_def_lang = await browser.storage.sync.get({default_chatgpt_lang: ''});
                     finalSubs['thunderai_def_lang'] = placeholdersUtils.failSafePlaceholders(prefs_def_lang.default_chatgpt_lang);
                     break;
+                case 'empty':
+                    finalSubs['empty'] = '';
+                    break;
                 default:    // TODO Manage custom placeholders https://github.com/micz/ThunderAI/issues/156
                     break;
             }