Fixed empty early widget returns

widgets/clientmenu/volume.lua

@@ -20,7 +20,7 @@ if _VERSION:match("5.1") then
     result = (test_pactl == 0)
 end
 if not result then
-    return
+    return function() end
 end
 
 local function get_icon(percent)

widgets/desktop/volume.lua

@@ -24,7 +24,7 @@ if _VERSION:match("5.1") then
     amixer_found = (test_amixer == 0)
 end
 if (not (amixer_found or pactl_found)) then
-    return
+    return function() end
 end
 
 local try_launch = "pavucontrol"