Make Creator compile without Qt tools in some configuration

Needing to compile Qt tools is a bit of a chore (and at some point a
diskspace issue) when building/starting Creator as sanity check for
comparing different compiler optimization settings.

This is not an officially supported configuration.

Change-Id: I628e33eb7137f09ecfebbd27453de548bac2fde5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/qtsupport/exampleslistmodel.cpp

@@ -104,8 +104,11 @@ ExampleSetModel::ExampleSetModel()
 
     connect(QtVersionManager::instance(), &QtVersionManager::qtVersionsLoaded,
             this, &ExampleSetModel::qtVersionManagerLoaded);
-    connect(Core::HelpManager::instance(), &Core::HelpManager::setupFinished,
-            this, &ExampleSetModel::helpManagerInitialized);
+
+    if (auto helpManager = Core::HelpManager::instance()) {
+        connect(helpManager, &Core::HelpManager::setupFinished,
+                this, &ExampleSetModel::helpManagerInitialized);
+    }
 }
 
 void ExampleSetModel::recreateModel()