Correct Frontlight status on suspend when screensaver mode is 'Leave … (#5928)

Also use a var in place of a long function name

frontend/device/generic/device.lua

@@ -230,8 +230,10 @@ function Device:onPowerEvent(ev)
         local UIManager = require("ui/uimanager")
         logger.dbg("Suspending...")
         -- Mostly always suspend in Portrait/Inverted Portrait mode...
-        -- ... except when we just show an InfoMessage, it plays badly with Landscape mode (c.f., #4098)
-        if G_reader_settings:readSetting("screensaver_type") ~= "message" then
+        -- ... except when we just show an InfoMessage or when the screensaver
+        -- is disabled, as it plays badly with Landscape mode (c.f., #4098 and #5290)
+        local screensaver_type = G_reader_settings:readSetting("screensaver_type")
+        if screensaver_type ~= "message" and screensaver_type ~= "disable" then
             self.orig_rotation_mode = self.screen:getRotationMode()
             -- Leave Portrait & Inverted Portrait alone, that works just fine.
             if bit.band(self.orig_rotation_mode, 1) == 1 then
@@ -244,9 +246,8 @@ function Device:onPowerEvent(ev)
             -- On eInk, if we're using a screensaver mode that shows an image,
             -- flash the screen to white first, to eliminate ghosting.
             if self:hasEinkScreen() and
-               G_reader_settings:readSetting("screensaver_type") == "cover" or
-               G_reader_settings:readSetting("screensaver_type") == "random_image" or
-               G_reader_settings:readSetting("screensaver_type") == "image_file" then
+               screensaver_type == "cover" or screensaver_type == "random_image" or
+               screensaver_type == "image_file" then
                 if not G_reader_settings:isTrue("screensaver_no_background") then
                     self.screen:clear()
                 end