Fix crash when on empty or invalid map.

When being on an invalid map, you used to get back to the initial spawning
point. This seems to have broken on a rewrite of the MapRenderer rendering
the object layer.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
MapRenderer: Orthogonal renderer also working correct with floating point

The r_cursor->map_pos.y is a float while the j and i are integers
and the intention is to check whether we're on the exact tile there,
so we need to cast the floats to int, to actually check only tile based.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Merge pull request #795 from stefanbeller/fixrendering

Fix crash when on empty or invalid map.