[FIX] snailmail: fix traceback on re-send or cancel failed letter, open \"Buy credits\" in new tab

PURPOSE

Fixes traceback when clicking on "re-send letter" or "cancel letter" buttons
(RPCs were being made with wrong number of arguments)
makes the "Buy credits" link open in a new tab to not interrupt the user's workflow

task-2068271

closes odoo/odoo#36667

Signed-off-by: Pierre Rousseau (pro) <pro@odoo.com>

addons/snailmail/static/src/js/message.js

@@ -21,7 +21,7 @@ Message.include({
         return this._rpc({
             model: 'mail.message',
             method: 'cancel_letter',
-            args: [[this.getID()], []],
+            args: [[this.getID()]],
         }).then(function () {
             self.setSnailmailStatus('canceled');
             self.setSnailmailError(false);
@@ -51,7 +51,7 @@ Message.include({
         return this._rpc({
             model: 'mail.message',
             method: 'send_letter',
-            args: [[this.getID()], []],
+            args: [[this.getID()]],
         });
     },
     /**

addons/snailmail/static/src/js/thread_widget.js

@@ -137,7 +137,7 @@ ThreadWidget.include({
             var content = _.str.sprintf(_t(
                 '<p>The letter could not be sent due to insufficient credits on your IAP account.</p>' +
                 '<div class= "text-right">' +
-                '<a class="btn btn-link buy_credits" href=%s>' +
+                '<a class="btn btn-link buy_credits" href=%s target="_blank">' +
                 '<i class= "fa fa-arrow-right"/> Buy credits' +
                 '</a>' +
                 '</div>'