Download the attachment as "attachment" if it fails due to a file I/O error

This can happen if the filename is invalid, ex:
https://bugs.archlinux.org/task/6698 contains a attachment with the
filename "." which wget can't write to:
.: Is a directory
Cannot write to '.' (Is a directory).

snapshotter.sh

@@ -76,8 +76,12 @@ function download_attachment() {
     mkdir -p "attachments/${1}/"{tmp,${2}}
     cd "attachments/${1}/tmp"
 
-    wget --content-disposition \
-         "https://bugs.archlinux.org/?getfile=${2}" || { [[ ${?} = 3 ]] && echo "Error downloading attachment: ${2}" && cd .. && rmdir tmp "${2}" && cd ../../ && return; }
+    options=(--content-disposition)
+    if [[ ${3:-false} = true ]]; then
+      options=(--output-document=attachment)
+    fi
+    wget "${options[@]}" \
+         "https://bugs.archlinux.org/?getfile=${2}" || { [[ ${?} = 3 ]] && echo "Error downloading attachment: ${2}" && cd .. && rmdir tmp "${2}" && cd ../../ || exit 1 && [[ ${3:-false} = true ]] && return; download_attachment "${1}" "${2}" "true"; return; }
     local files=(*)
     filename="${files[0]}"