comctl32/treeview: Fix possible crash in TVS_SINGELEXPAND helper (Coverity).

dlls/comctl32/tests/treeview.c

@@ -1255,6 +1255,13 @@ static void test_TVS_SINGLEEXPAND(void)
     ok(ret, "got %d\n", ret);
     ok_sequence(sequences, PARENT_SEQ_INDEX, parent_singleexpand_seq, "singleexpand notifications", FALSE);
 
+    /* a workaround for NT4 that sends expanding notification when nothing is about to expand */
+    ret = SendMessageA(hTree, TVM_DELETEITEM, 0, (LPARAM)hRoot);
+    ok(ret, "got %d\n", ret);
+    fill_tree(hTree);
+    ret = SendMessageA(hTree, TVM_SELECTITEM, TVGN_CARET, 0);
+    ok(ret, "got %d\n", ret);
+
     DestroyWindow(hTree);
 }
 

dlls/comctl32/treeview.c

@@ -3426,7 +3426,7 @@ static void TREEVIEW_SingleExpand(TREEVIEW_INFO *infoPtr,
 {
     TREEVIEW_ITEM *SelItem;
 
-    if ((infoPtr->dwStyle & TVS_SINGLEEXPAND) == 0 || infoPtr->hwndEdit) return;
+    if ((infoPtr->dwStyle & TVS_SINGLEEXPAND) == 0 || infoPtr->hwndEdit || !item) return;
 
     TREEVIEW_SendTreeviewNotify(infoPtr, TVN_SINGLEEXPAND, TVC_UNKNOWN, TVIF_HANDLE | TVIF_PARAM, item, 0);