Prevent null pointer deference in methods for selection.

This resolves the crash when exporting the Basket archive.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit a08c6ac9e3)

src/archive.cpp

@@ -228,7 +228,8 @@ void Archive::saveBasketToArchive(Basket *basket, bool recursive, KTar *tar, TQS
 
 	// Recursively save child baskets:
 	BasketListViewItem *item = Global::bnpView->listViewItemForBasket(basket);
-	if (recursive && item->firstChild()) {
+	if (recursive && item && item->firstChild())
+	{
 		for (BasketListViewItem *child = (BasketListViewItem*) item->firstChild(); child; child = (BasketListViewItem*) child->nextSibling()) {
 			saveBasketToArchive(child->basket(), recursive, tar, backgrounds, tempFolder, progress);
 		}

src/basket.cpp

@@ -4469,12 +4469,20 @@ void Basket::noteUngroup()
 
 void Basket::unplugSelection(NoteSelection *selection)
 {
+	if (!selection)
+	{
+		return;
+	}
 	for (NoteSelection *toUnplug = selection->firstStacked(); toUnplug; toUnplug = toUnplug->nextStacked())
 		unplugNote(toUnplug->note);
 }
 
 void Basket::insertSelection(NoteSelection *selection, Note *after)
 {
+	if (!selection)
+	{
+		return;
+	}
 	for (NoteSelection *toUnplug = selection->firstStacked(); toUnplug; toUnplug = toUnplug->nextStacked()) {
 		if (toUnplug->note->isGroup()) {
 			Note *group = new Note(this);
@@ -4496,6 +4504,10 @@ void Basket::insertSelection(NoteSelection *selection, Note *after)
 
 void Basket::selectSelection(NoteSelection *selection)
 {
+	if (!selection)
+	{
+		return;
+	}
 	for (NoteSelection *toUnplug = selection->firstStacked(); toUnplug; toUnplug = toUnplug->nextStacked()) {
 		if (toUnplug->note->isGroup())
 			selectSelection(toUnplug);