Fix int division bug when computing chunks for each dimension

The calls to Math.ceil were effectivly no-ops, as int/int produces an
int, which was then passed to the ceil method.

Author: lesserwhirls

cdm/zarr/src/main/java/ucar/nc2/iosp/zarr/ZarrHeader.java

@@ -397,7 +397,7 @@ private static int getChunkIndex(RandomAccessDirectoryItem item, ZArray zarray)
       int[] shape = zarray.getShape();
       int[] chunkSize = zarray.getChunks();
       for (int i = 0; i < nDims; i++) {
-        nChunks[i] = (int) Math.ceil(shape[i] / chunkSize[i]);
+        nChunks[i] = (int) Math.ceil((double) shape[i] / chunkSize[i]);
       }
       return ZarrUtils.subscriptsToIndex(subs, nChunks);
     } else {

cdm/zarr/src/main/java/ucar/nc2/iosp/zarr/ZarrLayoutBB.java

@@ -62,7 +62,7 @@ public ZarrLayoutBB(Variable v2, Section wantSection, RandomAccessFile raf) {
     for (int i = 0; i < ndims; i++) {
       Dimension dim = v2.getDimension(i);
       // round up nchunks if not evenly divisible by chunk size
-      this.nChunks[i] = (int) Math.ceil(dim.getLength() / this.chunkSize[i]);
+      this.nChunks[i] = (int) Math.ceil((double) dim.getLength() / this.chunkSize[i]);
       this.totalNChunks *= nChunks[i];
     }