[NTGDI] Silence some debug log spam from GreGetObjectOwner when input parameter is NULL. (reactos#7606)

CORE-19962
Co-authored-by: Timo Kreuzer <[email protected]>

Author: Doug-Lyons

win32ss/gdi/ntgdi/gdiobj.c

@@ -1193,6 +1193,12 @@ GreGetObjectOwner(HGDIOBJ hobj)
 {
     ULONG ulIndex, ulOwner;
 
+    if (hobj == NULL)
+    {
+        DPRINT("GreGetObjectOwner: invalid NULL handle\n");
+        return GDI_OBJ_HMGR_RESTRICTED;
+    }
+
     /* Get the handle index */
     ulIndex = GDI_HANDLE_GET_INDEX(hobj);