Bump base (#9618)

* Bump base (https://github.com/koreader/koreader-base/pull/1534)
* And some fixups following #9617

frontend/ui/uimanager.lua

@@ -824,7 +824,8 @@ function UIManager:sendEvent(event)
         if not checked_widgets[widget] then
             checked_widgets[widget] = true
             -- Widget's active widgets have precedence to handle this event
-            -- NOTE: ReaderUI & FileManager have their registered modules referenced as such.
+            -- NOTE: ReaderUI & FileManager *may* optionally register their modules as such
+            --       (currently, they only do that for the Screenshot module).
             if widget.active_widgets then
                 for _, active_widget in ipairs(widget.active_widgets) do
                     if active_widget:handleEvent(event) then

frontend/ui/widget/notification.lua

@@ -121,8 +121,8 @@ function Notification:init()
         RectSpan:new{
             -- have this VerticalGroup full width, to ensure centering
             width = Screen:getWidth(),
-            -- push this frame at its y=self.num position
-            height = notif_height * (self.num - 1) + self.margin,
+            -- push this frame at its y=self._shown_idx position
+            height = notif_height * (self._shown_idx - 1) + self.margin,
                 -- (let's add a leading self.margin to get the same distance
                 -- from top of screen to first notification top border as
                 -- between borders of next notifications)