Fix nether roof renders on Spigot 1.21.3

DynmapWorld.worldheight is reporting as 255 in 1.21.3, instead of 256 like it did before. (Overworld is now 319 -> 320). Unsure if this is a bug, since it seems right ...

Either way, do a Math.ceil to ensure there's enough sections even when the amount of blocks doesn't evenly line up with a 16 block section.

Author: jacob1

DynmapCore/src/main/java/org/dynmap/common/chunk/GenericMapChunkCache.java

@@ -618,8 +618,8 @@ public GenericMapChunkCache(GenericChunkCache c) {
 
 	public void setChunks(DynmapWorld dw, List<DynmapChunk> chunks) {
 		this.dw = dw;
-		nsect = (dw.worldheight - dw.minY) >> 4;
-		sectoff = (-dw.minY) >> 4;
+		nsect = (int)Math.ceil((dw.worldheight - dw.minY) / 16.0);
+		sectoff = (int)(Math.ceil((-dw.minY) / 16.0));
 		this.chunks = chunks;
 
 		/* Compute range */