tilesdl.cc: fix layout bug and crash with certain resolutions

This one was a pain to hunt down, but it was a surprisingly simple fix. Can you believe an X value was used where a Y value was needed?

Anyway, the bug was that with certain resolutions (i.e. 1440x900), the game would crash once the message list needed to be rendered.

And the layout was also completely wrong if you did something like an abnormal resolution of 800x850, which shows the message list near the middle of the screen instead of at the bottom.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>

Created by  Steven Noonan  on September 28, 2009
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