Disable irrelevant plugins on devices with no frontlight (#12766)

Closes #12764

plugins/autodim.koplugin/main.lua

@@ -5,6 +5,11 @@ Plugin for automatic dimming of the frontlight after an idle period.
 --]]--
 
 local Device = require("device")
+
+if not Device:hasFrontlight() then
+    return { disabled = true, }
+end
+
 local FFIUtil = require("ffi/util")
 local SpinWidget = require("ui/widget/spinwidget")
 local UIManager = require("ui/uimanager")

plugins/autowarmth.koplugin/_meta.lua

@@ -2,5 +2,5 @@ local _ = require("gettext")
 return {
     name = "autowarmth",
     fullname = require("device"):hasNaturalLight() and _("Auto warmth and night mode") or _("Auto night mode"),
-    description = _([[This plugin allows to set the frontlight warmth automagically.]]),
+    description = require("device"):hasNaturalLight() and _([[This plugin allows to set the frontlight warmth and night mode automagically.]]) or _([[This plugin allows to enable night mode automagically.]]),
 }