rpcrt4: Fix uninitialised memory read in ndr_marshall tests.

The memory needs to be initialised since NDR will look at the memory
to see if it needs to allocate memory for embedded pointers.

dlls/rpcrt4/tests/ndr_marshall.c

@@ -258,7 +258,7 @@ static void test_pointer_marshal(const unsigned char *formattypes,
 
     StubMsg.Buffer = StubMsg.BufferStart;
     StubMsg.MemorySize = 0;
-    mem_orig = mem = HeapAlloc(GetProcessHeap(), 0, size); 
+    mem_orig = mem = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, size);
 
     if(formattypes[1] & 0x10 /* FC_POINTER_DEREF */)
         *(void**)mem = NULL;