Cleared the “examine” message in the trade menu correctly

Cleared the “examine” message in the trade menu correctly.
Fixes more than 17 items trading. (you could not correctly trade the additional windows)
Fixes display for min height setting. (the last line wasn't shown, it is now).

Fixes: https://github.com/CleverRaven/Cataclysm-DDA/issues/270 and https://github.com/CleverRaven/Cataclysm-DDA/issues/6278 and https://github.com/CleverRaven/Cataclysm-DDA/issues/6277