core: preserve downloaded file in more cases [GH-4301]

CHANGELOG.md

@@ -19,6 +19,8 @@ IMPROVEMENTS:
 
 BUG FIXES:
 
+  - core: Downloading box files should resume in more cases since the
+      temporary file is preserved in more cases. [GH-4301]
   - core: Windows is not detected as NixOS in some cases. [GH-4302]
   - core: Fix encoding issues with Windows. There are still some outlying
       but this fixes a few. [GH-4159]

lib/vagrant/action/builtin/box_add.rb

@@ -435,10 +435,6 @@ module Vagrant
             # means we were interrupted as well.
             @download_interrupted = true
             env[:ui].info(I18n.t("vagrant.actions.box.download.interrupted"))
-          rescue Errors::DownloaderError
-            # The download failed for some reason, clean out the temp path
-            File.unlink(d.destination) if File.file?(d.destination)
-            raise
           end
 
           Pathname.new(d.destination)