BuildSteps: Fix a number of crashes

Fix crashes due to activeProjectConfigurationChanged signal sending
a nullptr.

Uses the same fix as QTCREATORBUG-18865, but in more places:-)

Task-number: QTCREATORBUG-18866
Change-Id: Ic71af5ed26b2a44339f0c687f3f46bfdf62c2489
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qbsprojectmanager/qbsproject.cpp

@@ -146,7 +146,7 @@ QbsProject::QbsProject(const FileName &fileName) :
     });
     connect(this, &Project::activeProjectConfigurationChanged,
             this, [this](ProjectConfiguration *pc) {
-        if (pc->isActive())
+        if (pc && pc->isActive())
             startParsing();
     });