user32: Avoid drawing the caret out of the window

[Bruno Jesus]

Please, ignore this patch. It's overkill to check the bounding box
during every caret timer callback. I have found a better approach to
this by checking inside SetCaretPos/ShowCaret. That's because the
caret doesn't move by itself so it's useless to check everytime.

Thanks,
Bruno

-- 
universe* god::bigbang (void); //and then it all began...