IAF dragon fix

Changelog
2.0.5
Changed
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Dragon roosts now require land. A candidate whose ocean-floor height is at or below sea level is rejected, so roosts no longer spawn on open water.
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Dragon caves are unaffected and still generate underground.
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The first-use /locate predictor applies the same land rule, so it never reports a roost that generation would later discard.
Notes
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The land check uses OCEAN_FLOOR_WG, which ignores water, so ocean columns correctly read as sea level or lower.