Fix battery status on the K4

And also probably prevent a crash when trying to enable WiFi there.
We really shouldn't even show the WiFi stuff on some of these old
devices, but at least now it doesn't crash ;).

frontend/device/kindle/device.lua

@@ -112,6 +112,11 @@ end
 
 function Kindle4:init()
     self.screen = require("ffi/framebuffer_einkfb"):new{device = self, debug = DEBUG}
+    self.powerd = require("device/kindle/powerd"):new{
+        device = self,
+        batt_capacity_file = "/sys/devices/system/yoshi_battery/yoshi_battery0/battery_capacity",
+        is_charging_file = "/sys/devices/platform/fsl-usb2-udc/charging",
+    }
     self.input = require("device/input"):new{
         device = self,
         event_map = require("device/kindle/event_map_kindle4"),

frontend/device/kindle/powerd.lua

@@ -11,8 +11,8 @@ local KindlePowerD = BasePowerD:new{
 }
 
 function KindlePowerD:init()
-    local lipc = require("liblipclua")
-    if lipc then
+    local haslipc, lipc = pcall(require, "liblipclua")
+    if haslipc and lipc then
         self.lipc_handle = lipc.init("com.github.koreader.kindlepowerd")
     end
     if self.device.hasFrontlight() then

frontend/ui/networkmgr.lua

@@ -8,9 +8,9 @@ local _ = require("gettext")
 local NetworkMgr = {}
 
 local function kindleEnableWifi(toggle)
-    local lipc = require("liblipclua")
+    local haslipc, lipc = pcall(require, "liblipclua")
     local lipc_handle = nil
-    if lipc then
+    if haslipc and lipc then
         lipc_handle = lipc.init("com.github.koreader.networkmgr")
     end
     if lipc_handle then