download_strategy: don't check url if already downloaded

Closes Homebrew/homebrew#40859.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/download_strategy.rb

@@ -270,16 +270,16 @@ class CurlDownloadStrategy < AbstractFileDownloadStrategy
   def fetch
     ohai "Downloading #{@url}"
 
-    urls = actual_urls
-    unless urls.empty?
-      ohai "Downloading from: #{urls.last}"
-      if !ENV["HOMEBREW_NO_INSECURE_REDIRECT"].nil? && @url.start_with?("https://") &&
-        urls.any? { |u| !u.start_with? "https://" }
-        raise "HTTPS to HTTP redirect detected & HOMEBREW_NO_INSECURE_REDIRECT is set."
+    unless cached_location.exist?
+      urls = actual_urls
+      unless urls.empty?
+        ohai "Downloading from: #{urls.last}"
+        if !ENV["HOMEBREW_NO_INSECURE_REDIRECT"].nil? && @url.start_with?("https://") &&
+          urls.any? { |u| !u.start_with? "https://" }
+          raise "HTTPS to HTTP redirect detected & HOMEBREW_NO_INSECURE_REDIRECT is set."
+        end
       end
-    end
 
-    unless cached_location.exist?
       had_incomplete_download = temporary_path.exist?
       begin
         _fetch