buildForwardAsAttachmentPayload intentionally returns an empty subject
for a subject-less email (matching normal Forward's composer-subject
behavior, fixed in 3bfa73f3), but this handler was reusing that same
empty string as the Pro compose tab's title. handleForward, right
above it, already computes its title with a fallback
(email.subject || t('email_composer.new_message')) before prefixing -
mirror that instead of reusing payload.subject for the title.
Caught by GitHub Copilot's automated PR review.