Idle detection: Fix crash on Wayland

Check for screen saver extension before using it, avoids a crash on
Wayland (where xcb_screensaver_query_info_reply returns null).

Change-Id: Icecd2f930ed071eff573866784c8c52ccc272253
Reviewed-on: https://codereview.kdab.com/c/Charm/+/88868
Reviewed-by: Andras Mantia <andras@kdab.com>
Tested-by: Continuous Integration <build@kdab.com>

diff --git a/Charm/Idle/IdleDetector.cpp b/Charm/Idle/IdleDetector.cpp
index 24e0c457..1cc74460 100644
--- Charm/Idle/IdleDetector.cpp
+++ Charm/Idle/IdleDetector.cpp
@@ -45,24 +45,22 @@ IdleDetector::IdleDetector(QObject *parent)
 IdleDetector *IdleDetector::createIdleDetector(QObject *parent)
 {
 #ifdef CHARM_IDLE_DETECTION
-#ifdef Q_OS_OSX
+#if (defined Q_OS_OSX)
     return new MacIdleDetector(parent);
-#endif
-
-#ifdef Q_OS_WIN
+#elif (defined Q_OS_WIN)
     return new WindowsIdleDetector(parent);
+#elif (defined CHARM_IDLE_DETECTION_AVAILABLE)
+    return new X11IdleDetector(parent);
+#else
+    auto unavailable = new IdleDetector(parent);
+    unavailable->setAvailable(false);
+    return unavailable;
 #endif
-
-#ifdef CHARM_IDLE_DETECTION_AVAILABLE
-    X11IdleDetector *detector = new X11IdleDetector(parent);
-    detector->setAvailable(detector->idleCheckPossible());
-    return detector;
-#endif
-#endif
-
-    IdleDetector *unavailable = new IdleDetector(parent);
+#else
+    auto unavailable = new IdleDetector(parent);
     unavailable->setAvailable(false);
     return unavailable;
+#endif
 }
 
 bool IdleDetector::available() const
diff --git a/Charm/Idle/X11IdleDetector.cpp b/Charm/Idle/X11IdleDetector.cpp
index 4f03a418..796742a3 100644
--- Charm/Idle/X11IdleDetector.cpp
+++ Charm/Idle/X11IdleDetector.cpp
@@ -32,18 +32,20 @@
 X11IdleDetector::X11IdleDetector(QObject *parent)
     : IdleDetector(parent)
 {
+    setAvailable(false);
+    m_connection = xcb_connect(NULL, NULL); // krazy:exclude=null
+    m_screen = xcb_setup_roots_iterator(xcb_get_setup(m_connection)).data;
+    if (!m_screen)
+        return;
+    auto query = xcb_get_extension_data(m_connection, &xcb_screensaver_id);
+    Q_ASSERT(query);
+    if (!query->present)
+        return;
+
     connect(&m_timer, &QTimer::timeout, this, &X11IdleDetector::checkIdleness);
     m_timer.start(idlenessDuration() * 1000 / 5);
     m_heartbeat = QDateTime::currentDateTime();
-}
-
-bool X11IdleDetector::idleCheckPossible()
-{
-    m_connection = xcb_connect(NULL, NULL); //krazy:exclude=null
-    m_screen = xcb_setup_roots_iterator(xcb_get_setup(m_connection)).data;
-    if (m_screen)
-        return true;
-    return false;
+    setAvailable(true);
 }
 
 void X11IdleDetector::onIdlenessDurationChanged()
diff --git a/Charm/Idle/X11IdleDetector.h b/Charm/Idle/X11IdleDetector.h
index 0b0f48ca..45ef9328 100644
--- Charm/Idle/X11IdleDetector.h
+++ Charm/Idle/X11IdleDetector.h
@@ -38,7 +38,6 @@ class X11IdleDetector : public IdleDetector
     Q_OBJECT
 public:
     explicit X11IdleDetector(QObject *parent);
-    bool idleCheckPossible();
 
 protected:
     void onIdlenessDurationChanged() override;
@@ -50,8 +49,8 @@ private Q_SLOTS:
     QDateTime m_heartbeat;
     QTimer m_timer;
 #if defined(Q_OS_UNIX) && !defined(Q_OS_OSX)
-    xcb_connection_t *m_connection;
-    xcb_screen_t *m_screen;
+    xcb_connection_t *m_connection = nullptr;
+    xcb_screen_t *m_screen = nullptr;
 #endif
 };