support tagged-devices in userExists in devmode

Even in dev mode, the user `tagged-devices` should not be
reported as existing user.

This allows editing & deleting links owned by `taggged-devices`
in dev mode.

Signed-off-by: Marco Hofstetter <marco.hofstetter@bluewin.ch>

golink.go

@@ -565,6 +565,10 @@ var currentUser = func(r *http.Request) (string, error) {
 func userExists(ctx context.Context, login string) (bool, error) {
 	const userTaggedDevices = "tagged-devices" // owner of tagged devices
 
+	if login == userTaggedDevices {
+		return false, nil
+	}
+
 	if devMode() {
 		// in dev mode, just assume the user exists
 		return true, nil