Debugger: Fix thread switcher combobox to show current thread

When a breakpoint was hit, the combo box "popup" correctly showed
which thread was interrupted (with the little left-arrow icon),
but the actual combo box always showed the first thread.

This change makes sure to update the combo box current index whenever
a breakpoint is hit.

Change-Id: I8339f4334df46830f5e8f82a2b4eafa9e6a388c4
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/threadshandler.cpp

@@ -408,6 +408,11 @@ void ThreadsHandler::setThreads(const GdbMi &data)
 
     if (!m_currentThread && threads.childCount() > 0)
         m_currentThread = rootItem()->childAt(0);
+
+    if (!m_currentThread) {
+        const QModelIndex currentThreadIndex = m_currentThread->index();
+        threadSwitcher()->setCurrentIndex(currentThreadIndex.row());
+    }
 }
 
 QAbstractItemModel *ThreadsHandler::model()