retryable_download: ensure HOMEBREW_CELLAR exists.

Author: MikeMcQuaid

Library/Homebrew/retryable_download.rb

@@ -73,6 +73,7 @@ def fetch(verify_download_integrity: true, timeout: nil, quiet: false)
       downloadable.verify_download_integrity(download) if verify_download_integrity && !json_download
 
       if pour && downloadable.is_a?(Bottle)
+        HOMEBREW_CELLAR.mkpath
         UnpackStrategy.detect(download, prioritize_extension: true)
                       .extract_nestedly(to: HOMEBREW_CELLAR)
       elsif json_download