[mkgmap-dev] mkgmap r4048 seems to fix problem with hill shading

Hi all, I've changed the code so that when a sub tile (typically 64x64) is completely outside of the polygon (--dem-poly) is still encoded with a bit stream. This is how BuildDEMFile does it and it seems that this solves all problems reported by Andrzej. Before this I simply wrote a header that said "no bit stream, all heights are equal, highest value is invalid", but Garmin doesn't seem to like that. The change means that a few more bytes are written to DEM, maybe also runtime is a bit higher. Gerd