Fixed GlobalSize return value for zero size block.

diff --git a/memory/heap.c b/memory/heap.c
index 2e3f580..2264fef 100644
--- a/memory/heap.c
+++ b/memory/heap.c
@@ -1204,7 +1204,7 @@
  *           HeapSize   (KERNEL32.341)
  * RETURNS
  *	Size in bytes of allocated memory
- *	0: Failure
+ *	0xffffffff: Failure
  */
 DWORD WINAPI HeapSize(
              HANDLE32 heap, /* [in] Handle of heap */