Kindle: Make ReaderActivityIndicator a stub (#7002)

And only actually flesh it out and register it in the very few cases
where it can actually do something (i.e., old FW 5.x with KPV).

frontend/apps/reader/modules/readeractivityindicator.lua

@@ -1,16 +1,43 @@
-local EventListener = require("ui/widget/eventlistener")
+-- Start with a empty stub, because 99.9% of users won't actually need this.
+local ReaderActivityIndicator = {}
+
+function ReaderActivityIndicator:isStub() return true end
+function ReaderActivityIndicator:init() end
+function ReaderActivityIndicator:onStartActivityIndicator() end
+function ReaderActivityIndicator:onStopActivityIndicator() end
+function ReaderActivityIndicator:coda() end
+
+-- Now, if we're on Kindle, and we haven't actually murdered Pillow, see what we can do...
 local Device = require("device")
+
+if Device:isKindle() then
+    if os.getenv("PILLOW_HARD_DISABLED") or os.getenv("PILLOW_SOFT_DISABLED") then
+        -- Pillow is dead, bye!
+        return ReaderActivityIndicator
+    end
+
+    if not Device:isTouchDevice() then
+        -- No lipc, bye!
+        return ReaderActivityIndicator
+    end
+else
+    -- Not on Kindle, bye!
+    return ReaderActivityIndicator
+end
+
+
+-- Okay, if we're here, it's basically because we're running on a Kindle on FW 5.x under KPV
+local EventListener = require("ui/widget/eventlistener")
 local util = require("ffi/util")
 -- lipc
 
-local ReaderActivityIndicator = EventListener:new{}
+function ReaderActivityIndicator:isStub() return false end
+
+ReaderActivityIndicator = EventListener:new{}
 
 function ReaderActivityIndicator:init()
-    local dev_mod = Device.model
-    if dev_mod == "KindlePaperWhite" or dev_mod == "KindlePaperWhite2" or dev_mod == "KindleVoyage" or dev_mod == "KindleBasic" or dev_mod == "KindlePaperWhite3" or dev_mod == "KindleOasis" or dev_mod == "KindleBasic2" or dev_mod == "KindleTouch" then
-        if (pcall(require, "liblipclua")) then
-            self.lipc_handle = lipc.init("com.github.koreader.activityindicator")
-        end
+    if (pcall(require, "liblipclua")) then
+        self.lipc_handle = lipc.init("com.github.koreader.activityindicator")
     end
 end