CodeGenerated collision has extra lip

[TokisanGames]

Description

The code generated scene has an extra collision lip, though it is not present in the non-code generated demo. 0.9.1-beta.

[TokisanGames]

The demo noise makes the terrain dip below 0 on the +X,+Z edges.

The collision lip is caused by _update_collision where it assumes the next +x and +z map values are 0 if they don't exist. On the +X,+Z edge of the world, the next maps don't exist, so 0 is used. In the current version, the shader also matches the collision so there are both visual and collision lips. We could fix collision easily by using the last height, but it's not so easy for the shader. So, now that they match, I won't change them.

What I will do is increase the height of the demo terrain so it is above 0 on the +X, +Z edges. Completed in fba0242