[Patch] Possible of bounds access to TaskModel::m_tasks

In this downstream bug report at redhat bugzilla, a user reports the following crash:

#0  Task (this=0x7fffc42464b0) at task.h:47
#1  ProjectExplorer::Internal::TaskModel::task (this=0xd9d7a0, index=...) at taskmodel.cpp:269
#2  0x00007fc6662ca6bf in ProjectExplorer::Internal::TaskWindow::currentChanged (this=0xda44b0, index=...) at taskmodel.h:159

(see here for full trace)

The (not very detailed) description of the circumstances was "I restarted a build with -j24 after cancelling the previos -j12 build".

This looks like an out of bounds access to m_tasks in the function

Task TaskModel::task(const QModelIndex &index) const
{
    if (!index.isValid())
        return Task();
    return m_tasks.at(index.row());
}

Looking briefly at the code, I see that in other location, the index row is also validated (as opposed to only the index), for instance

bool TaskModel::hasFile(const QModelIndex &index) const
{
    int row = index.row();
    if (!index.isValid() || row < 0 || row >= m_tasks.count())
        return false;
    return !m_tasks.at(row).file.isEmpty();
}

I guess the same checks could also be performed in TaskModel::task, see attached proposed patch.

Note that I was not able to reproduce the issue, and possibly there is a deeper issue as to why the index row is invalid in the first place.