CppEditor: Cancel runner in ~CppUseSelectionsUpdater

...otherwise an already destructed QTextDocument might be accessed in
the ClangCodeModel::Internal::IpcReceiver::references.

Task-number: QTCREATORBUG-18459
Change-Id: I1868b2fd3a64341794f83eea6c4eeb7c2c1af812
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cppeditor/cppuseselectionsupdater.cpp

@@ -49,6 +49,12 @@ CppUseSelectionsUpdater::CppUseSelectionsUpdater(TextEditor::TextEditorWidget *e
     connect(&m_timer, &QTimer::timeout, this, [this]() { update(); });
 }
 
+CppUseSelectionsUpdater::~CppUseSelectionsUpdater()
+{
+    if (m_runnerWatcher)
+        m_runnerWatcher->cancel();
+}
+
 void CppUseSelectionsUpdater::scheduleUpdate()
 {
     m_timer.start();