Avoid overflowing allocation size in CallMalloc()

The wraparound could happen if USE_MAGIC_HEADERS is enabled.
static LPVOID ChkedTlsGetValue(DWORD idx)
{
	LPVOID ret=TlsGetValue(idx);
	assert(S_OK==GetLastError());
	return ret;
}

static LPVOID ChkedTlsGetValue(DWORD idx)
{
	LPVOID ret=TlsGetValue(idx);
	assert(S_OK==GetLastError());
	return ret;
}
