win: Fix a few minor issues found by clang.

sandbox/src/sandbox_nt_util.cc

Index: sandbox/src/sandbox_nt_util.cc
diff --git a/sandbox/src/sandbox_nt_util.cc b/sandbox/src/sandbox_nt_util.cc
index e730ddb98cae4b4b14a8a8d909940b0fc964752d..605fceea9e97d145acf90a42b83b320f6fea70c6 100644
--- a/sandbox/src/sandbox_nt_util.cc
+++ b/sandbox/src/sandbox_nt_util.cc
@@ -538,7 +538,7 @@ void* operator new(size_t size, sandbox::AllocationType type,
 
   if (NT_ALLOC == type) {
     if (!InitHeap())
-      return false;
+      return NULL;
 
     // Use default flags for the allocation.
     return g_nt.RtlAllocateHeap(sandbox::g_heap, 0, size);