[mpv] Fix battery script on desktop PC

Fixed requiring a battery or receiving an error. Script will simply set
high quality mode on desktop.

mpv/.config/mpv/scripts/battery.lua

@@ -4,7 +4,10 @@ local lqprofile = "lowquality"
 local hqprofile = "highquality"
 
 local function powerstate()
-  local f = assert(io.open("/sys/class/power_supply/AC/online"))
+  local f =io.open("/sys/class/power_supply/AC/online")
+  if f == nil then
+    return
+  end
   local t = f:read("*n")
   f:close()
   return t