ReaderFooter: Smarter hardware event handlers

Make sure we don't repaint the footer over anything else than ReaderUI,
as some events are fired without direct UI interaction, so we can't be
assured of the actual state of the UI.

Fix #7556

Exposed since #7379, but could arguably happen with other existing
handlers before.

frontend/apps/reader/modules/readerfooter.lua

@@ -1873,14 +1873,6 @@ function ReaderFooter:onUpdateFooter(force_repaint, force_recompute)
     end
 end
 
-function ReaderFooter:onCharging()
-    self:onUpdateFooter(self.view.footer_visible)
-end
-
-function ReaderFooter:onNotCharging()
-    self:onUpdateFooter(self.view.footer_visible)
-end
-
 function ReaderFooter:updateFooterPage(force_repaint, force_recompute)
     if type(self.pageno) ~= "number" then return end
     if self.ui.document:hasHiddenFlows() then
@@ -2230,24 +2222,42 @@ function ReaderFooter:onCloseDocument()
     self:unscheduleFooterAutoRefresh()
 end
 
+-- Used by event handlers that can trip without direct UI interaction...
+function ReaderFooter:maybeUpdateFooter()
+    -- ...so we need to avoid stomping over unsuspecting widgets (usually, ScreenSaver).
+    if UIManager:getTopWidget() == "ReaderUI" then
+        self:onUpdateFooter(self.view.footer_visible)
+    else
+        self:onUpdateFooter()
+    end
+end
+
 function ReaderFooter:onFrontlightStateChanged()
     if self.settings.frontlight then
-        self:onUpdateFooter(true)
+        self:maybeUpdateFooter()
     end
 end
 
 function ReaderFooter:onNetworkConnected()
     if self.settings.wifi_status then
-        self:onUpdateFooter(true)
+        self:maybeUpdateFooter()
     end
 end
 
 function ReaderFooter:onNetworkDisconnected()
     if self.settings.wifi_status then
-        self:onUpdateFooter(true)
+        self:maybeUpdateFooter()
     end
 end
 
+function ReaderFooter:onCharging()
+    self:maybeUpdateFooter()
+end
+
+function ReaderFooter:onNotCharging()
+    self:maybeUpdateFooter()
+end
+
 function ReaderFooter:onSetRotationMode()
     self:updateFooterContainer()
     self:resetLayout(true)