Cancel a download job when deleted from web UI

src/mangadex/downloader.cr

@@ -91,6 +91,7 @@ module MangaDex
           end
 
           channel.send page_job
+          break unless @queue.exists? job
         end
       end
 
@@ -98,6 +99,9 @@ module MangaDex
         page_jobs = [] of PageJob
         chapter.pages.size.times do
           page_job = channel.receive
+
+          break unless @queue.exists? job
+
           Logger.debug "[#{page_job.success ? "success" : "failed"}] " \
                        "#{page_job.url}"
           page_jobs << page_job
@@ -110,6 +114,13 @@ module MangaDex
             Logger.error msg
           end
         end
+
+        unless @queue.exists? job
+          Logger.debug "Download cancelled"
+          @downloading = false
+          next
+        end
+
         fail_count = page_jobs.count { |j| !j.success }
         Logger.debug "Download completed. " \
                      "#{fail_count}/#{page_jobs.size} failed"