Fix crash: use UIManager:close() instead of non-existent closeAllDialogs

main.lua

@@ -511,9 +511,10 @@ function Bookhoard:startRegistration()
 
         self.registration_id = result.registration_id
 
-        UIManager:show(InfoMessage:new{
+        self.waiting_dialog = InfoMessage:new{
             text = T(_("Device registered on server.\n\nOpen your Bookhoard web UI and go to:\n%1/devices\n\nApprove this device in the \"Pending Device Registrations\" section.\n\nWaiting for approval…"), self.settings.server_url),
-        })
+        }
+        UIManager:show(self.waiting_dialog)
 
         self:startRegistrationPoll()
     end)
@@ -551,7 +552,10 @@ function Bookhoard:startRegistrationPoll()
             self.settings.sync_endpoints = result.sync_endpoints
             G_reader_settings:saveSetting(self.settings_key, self.settings)
             self:registerEvents()
-            UIManager:closeAllDialogs()
+            if self.waiting_dialog then
+                UIManager:close(self.waiting_dialog)
+                self.waiting_dialog = nil
+            end
             UIManager:show(InfoMessage:new{
                 text = _("Device registered successfully!"),
                 timeout = 3,