Create fallback page for iOS browsers failing to open Tailscale login…

… page (#198)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

tailscale/rootfs/etc/nginx/templates/ingress.gtpl

@@ -11,6 +11,7 @@ server {
         proxy_pass http://backend;
 
         sub_filter_once off;
-        sub_filter 'document.location.href = url' 'window.open(url, "_blank").focus()';
+        sub_filter 'document.location.href = url' 'var result = window.open(url, "_blank"); if (result!== null) {result.focus()} else {document.write(\'<div style="background-color:white"><font color=black>Unable to open Tailscale in new window.  Please copy this URL, open it in a separate browser, and re-load the addon Web UI here when complete.   <a href="\' + url + \'">\'+url+\'</a></font></div>\')}';
+
     }
 }