MgCooker: Tile count completely wrong when override coordinates specified

[jng]

1. Select the Sheboygan tiled map
2. Start a tiling session. Observe that it has about 1.7 million tiles to process.
3. Stop the session and override its coordinates, cut down a few decimal places.
4. Re-run the tiling session. The session ends immediately, and most likely the calculated total is 0 or some very small number.