Fix harmless g++ warning about "using NULL in arithmetic".

::SetThreadExecutionState() returns a DWORD, which is not a pointer, so
compare its return value with 0, not NULL.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77746 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/power.cpp

@@ -59,7 +59,7 @@ bool UpdatePowerResourceExecutionState()
     if ( g_powerResourceSystemRefCount > 0 )
         executionState |= ES_SYSTEM_REQUIRED;
 
-    if ( ::SetThreadExecutionState(executionState) == NULL )
+    if ( ::SetThreadExecutionState(executionState) == 0 )
     {
         wxLogLastError(wxT("SetThreadExecutionState()"));
         return false;