emails: fix sending emails to invalid addresses.

Fix mailers to not attempt deliveries to invalid or nonexistent email
addresses. This usually happened when someone changed their email, and
we tried to send a confirmation email to a nonexistent address.

app/mailers/application_mailer.rb

@@ -5,4 +5,11 @@
 # @see https://guides.rubyonrails.org/action_mailer_basics.html
 class ApplicationMailer < ActionMailer::Base
   default from: "#{Danbooru.config.canonical_app_name} <#{Danbooru.config.contact_email}>", content_type: "text/html"
+
+  def mail(user, require_verified_email:, **options)
+    to = email_address_with_name(user.email_address&.address, user.name)
+    message = super(to: to, **options)
+    message.perform_deliveries = user.can_receive_email?(require_verified_email: require_verified_email)
+    message
+  end
 end