Test app tarball before removing old app version

templates/nextcloud-onlyoffice-config.yaml

@@ -141,6 +141,10 @@ data:
       # allows us to use version variable in the release_filename
       {{- $_ := set $ "version" .version}}
       curl "https://github.com/{{ .github_repository }}/releases/download/{{ .version }}/{{ tpl .release_filename $ }}" -Lo "{{ .name }}.tar.gz"
+      # If the above url results in a 404, curl will not complain and store the
+      # body of the 404 in the file :/. So we check here whether we actually
+      # got a valid archive; `tar` will fail if not.
+      tar -tf "{{ .name }}.tar.gz"
       # Remove old version of the app
       if [[ -d "$target_directory/{{ .name }}" ]]
       then