[PATCH] RealizePalette should return GDI_ERROR not 0

according to http://msdn.microsoft.com/de-de/library/windows/desktop/dd162896(v=vs.85).aspx
RealizePalette returns GDI_ERROR on failure. In ReactOS it returns 0.
Corrected the if-Statement in painting.c from "!= 0" to "> 0"