Guard push against no document open

main.lua

@@ -884,6 +884,16 @@ function Bookhoard:updateProgress(ensure_networking, interactive)
 
     if not self.settings.sync_progress then return end
 
+    if not self.ui.document then
+        if interactive then
+            UIManager:show(InfoMessage:new{
+                text = _("No document open."),
+                timeout = 3,
+            })
+        end
+        return
+    end
+
     local now = UIManager:getElapsedTimeSinceBoot()
     if not interactive and now - self.push_timestamp <= API_CALL_DEBOUNCE_DELAY then
         return