Partial rerendering: really avoid flash on reload (#10155)

Also restore input if ReaderUI crashed.
Also avoid refresh_count management when "Full refresh
rate" is set to "never".

frontend/apps/reader/readerui.lua

@@ -608,6 +608,9 @@ function ReaderUI:showReaderCoroutine(file, provider, seamless)
         if err ~= nil or ok == false then
             io.stderr:write('[!] doShowReader coroutine crashed:\n')
             io.stderr:write(debug.traceback(co, err, 1))
+            -- Restore input if we crashed before ReaderUI has restored it
+            Device:setIgnoreInput(false)
+            Input:inhibitInputUntil(0.2)
             UIManager:show(InfoMessage:new{
                 text = _("No reader engine for this file or invalid file.")
             })
@@ -617,6 +620,9 @@ function ReaderUI:showReaderCoroutine(file, provider, seamless)
 end
 
 function ReaderUI:doShowReader(file, provider, seamless)
+    if seamless then
+        UIManager:avoidFlashOnNextRepaint()
+    end
     logger.info("opening file", file)
     -- Only keep a single instance running
     if ReaderUI.instance then

frontend/ui/uimanager.lua

@@ -1123,7 +1123,7 @@ function UIManager:_refresh(mode, region, dither)
     --       (Putting "ui" in that list is problematic with a number of UI elements, most notably, ReaderHighlight,
     --       because it is implemented as "ui" over the full viewport, since we can't devise a proper bounding box).
     --       So we settle for only "partial", but treating full-screen ones slightly differently.
-    if mode == "partial" and not self.refresh_counted then
+    if mode == "partial" and self.FULL_REFRESH_COUNT > 0 and not self.refresh_counted then
         self.refresh_count = (self.refresh_count + 1) % self.FULL_REFRESH_COUNT
         if self.refresh_count == self.FULL_REFRESH_COUNT - 1 then
             -- NOTE: Promote to "full" if no region (reader), to "flashui" otherwise (UI)
@@ -1290,6 +1290,11 @@ function UIManager:forceRePaint()
     self:_repaint()
 end
 
+function UIManager:avoidFlashOnNextRepaint()
+    -- Avoid going through the "partial" to "full" refresh promotion: pretend we already checked that.
+    self.refresh_counted = true
+end
+
 --[[--
 Ask the EPDC to *block* until our previous refresh ioctl has completed.