Don't emit signals when clearing selection and signals are blocked

Currently in my project (http://nano.yandex.ru/project/online/) I
employ a pretty harsh way of using a model.

When QSortFilterProxyModel in Qt 4.3 re-sorts
everything every time it is very processor-hungry. So I have
implement some hacks in order to boost performance, like after big
updates I either do reset() + layoutAboutToBeChanged() +
layoutChanged(), or layoutAboutToBeChanged() + layoutChanged(), and it
could lead to very bad stuff happening.

One of the crashes I've got because after I try to clear
QItemSelectionModel it tries to gather some data in order to send a
proper selectionChanged() signal. I then tried to work-around this by
blocking signals altogether, but it didn't work because it still uses
now-incorrect QModelIndexes at the data-gathering period, so I
produced this patch:

diff -urN qt-x11-opensource-src-4.3.5.orig/src/gui/itemviews/qitemselectionmodel.cpp qt-x11-opensource-src-4.3.5/src/gui/itemviews/qitemselectionmodel.cpp
— qt-x11-opensource-src-4.3.5.orig/src/gui/itemviews/qitemselectionmodel.cpp 2008-09-02 16:12:14.000000000 +0400
+++ qt-x11-opensource-src-4.3.5/src/gui/itemviews/qitemselectionmodel.cpp 2008-09-02 18:08:15.000000000 +0400
@@ -1058,10 +1058,14 @@
if (d->ranges.count() == 0 && d->currentSelection.count() == 0)
return;
QItemSelection selection = d->ranges;

• selection.merge(d->currentSelection, d->currentCommand);
  + if (!signalsBlocked()) { + selection.merge(d->currentSelection, d->currentCommand); + }

  d->ranges.clear();
  d->currentSelection.clear();

• emit selectionChanged(QItemSelection(), selection);
  + if (!signalsBlocked()) { + emit selectionChanged(QItemSelection(), selection); + }

  }