naughty: check workarea in get_offset, not at load

Signed-off-by: koniu <gkusnierz@gmail.com>

lib/naughty.lua.in

@@ -91,8 +91,6 @@ notifications = {
     bottom_right = {},
 }
 
-local ws = capi.screen[config.screen].workarea
-local ss = capi.screen[config.screen].geometry
 
 --- Evaluate desired position of the notification by index - internal
 -- @param idx Index of the notification
@@ -101,6 +99,7 @@ local ss = capi.screen[config.screen].geometry
 -- @return Absolute position in {x, y} dictionary
 
 local function get_offset(idx, position, lines)
+    local ws = capi.screen[config.screen].workarea
     local v = {}
 
     -- calculate x