kindle: fix possible crash when not connected to a network but wifi is on (koreader#15519)

Author: benoit-pierre

frontend/device/kindle/device.lua

@@ -500,8 +500,8 @@ function Kindle:initNetworkManager(NetworkMgr)
                 signal_level = string.format("%d/%d", network.signal, network.signal_max),
                 signal_quality = qualities[network.signal],
                 -- See comment above about netid being unfortunately optional...
-                connected = (current_profile.netid and current_profile.netid ~= -1 and current_profile.netid == network.netid)
-                         or (current_profile.netid == nil and current_profile.essid ~= "" and current_profile.essid == network.essid),
+                connected = current_profile and ((current_profile.netid and current_profile.netid ~= -1 and current_profile.netid == network.netid)
+                         or (current_profile.netid == nil and current_profile.essid ~= "" and current_profile.essid == network.essid)),
                 flags = network.key_mgmt,
                 ssid = network.essid ~= "" and network.essid,
                 password = password,