Using Track Block Get Previous

Pasted from gitter.

Track blocks are what you place when you use the ride construction window i.e. they can be made up of multiple map elements. I know for your function its only one element but we should use track block get previous as it adds some protection. You have to pass the x and y coordinates of the start of the track block and the map_element of the tile. I suggest doing it like thus:

rct_map_element* trackElement =
map_get_track_element_at_of_type_seq(
                    x,
                    y,
                    z / 8,
                    trackType,
                    0);

rct_xy_element input;

input.x = x;
input.y = y;
input.element = trackElement;
track_begin_end output;

The output is a track_begin_end structure. The track_begin_end structure should in theory give x, y coordinates of the start and end of a track block and the map_element's associated with either end. In general you should only concern yourself with the begin variables.

Now using track_block_get_previous is pretty simple. It returns false if it fails to find the next track block and true if it does find another block. On failure do not trust the contents of the output.