Provide a sane error message in case dialog is not installed

(cherry picked from commit ea233da43a)

mutt-wizard.sh

@@ -257,5 +257,6 @@ $(grep ~/.offlineimaprc -e "^accounts =" | sed 's/accounts =//g')
 5) inventory && for i in $userchoices; do removeAccount $i ; done;;
 6) (dialog --defaultno --title "Wipe all custom neomutt/offlineIMAP settings?" --yesno "Would you like to wipe all of the mutt/offlineIMAP settings generated by the system?" 6 60 && wipe) ;;
 7) clear && break ;;
+*) echo "Unable to read response from dialog. Exiting." >&2; exit 2
 esac
 done