Bug fix: bridge graphics

[Phystam]

Hi james,

Now I think that I have fixed the bridge graphics problem if the bridge has own way graphics.
the problem was from calc_image() function in boden/wege/weg.cc. While the way checks whether it is on the bridge in Standard code, the way does not check it in Extended code despite it is necessary for "has_own_way_graphics" flag.

the github repository is here: https://github.com/Phystam/Simutrans-Extended/tree/bridge-draw

before:


after:

[jamespetts]

Thank you very much for this and apologies for not being able to look into this before: I have only recently got my new computer running. I have now incorporated this. Thank you again.