bug fix: request to WCS server should be limited to extent of data it has for the layer, or the request may fail. See https://forum.worldwindcentral.com/forum/world-wind-java-forums/development-help/158241-wcs-elevation-model-with-partial-data.

Author: gbburkhardt

src/gov/nasa/worldwind/terrain/BasicElevationModel.java

@@ -385,6 +385,8 @@ protected ElevationTile createTile(TileKey key)
         Angle minLongitude = ElevationTile.computeColumnLongitude(key.getColumn(), dLon, lonOrigin);
 
         Sector tileSector = new Sector(minLatitude, minLatitude.add(dLat), minLongitude, minLongitude.add(dLon));
+        // Clip tile sector by the layer's coverage extent
+        tileSector = levels.getSector().intersection(tileSector);
 
         return new ElevationTile(tileSector, level, key.getRow(), key.getColumn());
     }