fix(install): Fix aria2's resume download feature

[Retia-Adolf]

1. $has_downloads, I can't get what this means, probably "has to download"? so I used another var $download_finished instead.

2. When

   test-path cache\filename.ext 		-> true,
   test-path cache\filename.ext.aria2	-> true,
   test-path cache\app.txt 			-> true,
   

   it indicates download had started but not finished, since otherwise app.txt, filename.ext.aria2 should be removed each by function dl_with_cache_aria2, aria2 process.

   So only when

   test-path cache\filename.ext		 -> true,
   test-path cache\filename.ext.aria2	 -> false,
   test-path cache\app.txt				 -> false,
   

   indicates $download_finished = $true, it does not need to download again, this time should it load cached file.