[FIX] mail: temporary id should be negative

Before this commit temporary id could match an existing attachment id and
replace that attachment by the new uploaded one.
Even if this is very unlikly, using a negative id avoid it completly.

closes odoo/odoo#82185

X-original-commit: c18705d1ced6a9b1d6bb8c33049a1248ae83cf18
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/components/file_uploader/file_uploader.js

@@ -12,7 +12,7 @@ const { useRef } = owl.hooks;
 const geAttachmentNextTemporaryId = (function () {
     let tmpId = 0;
     return () => {
-        tmpId += 1;
+        tmpId -= 1;
         return tmpId;
     };
 })();