[PATCH] Drop-down lists are not reinitialized properly.

[Deiz]

As the HandleMessage functions all return void, there's no way to easily determine whether a dropdown's child list has been modified after handling a message.

For a demonstration of the issue at present, go to set up a match, change the map selection filter to "Old Maps" - notice the dropdown is still large despite there being zero maps. Now, change back to 'Default' and notice it's only showing one map.

More or less, the buggy behaviour results in the dropdown rectangle's size lagging until it has been assigned to twice.

Having the list track when it's updated its items allows the dropdown to detect the modification and reinitialize the list size properly.

[Deiz]

In 12244:

Properly re-initialize drop-down lists when the list items changes. Fixes #1558.