On GlobalHeap instantiation, we should stop reading file data just af…

…ter we met a HeapObject.id equals to 0. Otherwise, we could be at the end of the file and a EOFException will be raised. Addresses the github issue Unidata#532.

cdm/core/src/main/java/ucar/nc2/internal/iosp/hdf5/H5objects.java

@@ -2626,6 +2626,8 @@ class GlobalHeap {
  long startPos = raf.getFilePointer();
  GlobalHeap.HeapObject o = new GlobalHeap.HeapObject();
  o.id = raf.readShort();
+ if (o.id == 0)
+ break; // ?? look
  o.refCount = raf.readShort();
  raf.skipBytes(4);
  o.dataSize = header.readLength();
@@ -2634,8 +2636,6 @@ class GlobalHeap {
  int dsize = ((int) o.dataSize) + padding((int) o.dataSize, 8);
  countBytes += dsize + 16;
 
- if (o.id == 0)
- break; // ?? look
  if (o.dataSize < 0)
  break; // ran off the end, must be done
  if (countBytes < 0)