console.lua: fix completing empty --dscale and --cscale

These options accept an empty value within their choices. If the user
didn't add manually input a quote before completing them, add quotes
automatically so that the blank value can actually be used.

player/lua/console.lua

@@ -1220,6 +1220,11 @@ local function handle_choice_completion(option, before_cur, path_pos)
         return handle_file_completion(before_cur, path_pos)
     end
 
+    -- Fix completing the empty value for --dscale and --cscale.
+    if info.choices and info.choices[1] == '' and completion_append == '' then
+        info.choices[1] = '""'
+    end
+
     return info.choices, before_cur
 end