Return false if index is out of bounds in GetItemT.

diff --git a/dlls/comctl32/header.c b/dlls/comctl32/header.c
index f961122..4b533fc 100644
--- a/dlls/comctl32/header.c
+++ b/dlls/comctl32/header.c
@@ -813,11 +813,10 @@
 
     if (phdi->mask == 0)
 	return TRUE;
-
     if ((nItem < 0) || (nItem >= (INT)infoPtr->uNumItem))
-        lpItem = NULL;
-    else
-        lpItem = &infoPtr->items[nItem];
+        return FALSE;
+
+    lpItem = &infoPtr->items[nItem];
 
     if (phdi->mask & HDI_BITMAP)
 	phdi->hbm = (lpItem != NULL) ? lpItem->hbm : 0;