Zoom setting does not reset when scenario is reloaded.

[gbrawn]

Upon reloading a scenario when completed, the session gui should reset the zoom setting (denoted by ++++ in the .scn file), currently it adds the zoom setting to the current zoom setting. e.g. if zoom setting is ++ in .scn file, reloading the .scn file in the current gui session sets the zoom setting to ++ then ++ = ++++.