(svn r13348) -Fix: an industry does not always need foundations; in the case of NewGRFs an industry can be built on a steep slope, however when 'querying' the foundation type of an industry we neglected the fact that these steep slope tiles do not have a foundation. As a result of this when one built a structure requiring foundations on a tile SW or SE of a steep slope industry tile it would try to apply the foundation on the steep slope to determine whether to draw the wall of the foundation and trigger an assert.

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