toolChain() might return a null pointer

Don't crash then

src/plugins/qt4projectmanager/projectloadwizard.cpp

@@ -122,7 +122,6 @@ void ProjectLoadWizard::addBuildConfiguration(QString name, QtVersion *qtversion
         m_project->setQtVersion(name, 0);
     else
         m_project->setQtVersion(name, qtversion->uniqueId());
-
 }
 
 void ProjectLoadWizard::done(int result)

src/plugins/qt4projectmanager/qt4project.cpp

@@ -400,12 +400,14 @@ ProjectExplorer::ToolChain *Qt4Project::toolChain(const QString &buildConfigurat
 
 QString Qt4Project::makeCommand(const QString &buildConfiguration) const
 {
-    return toolChain(buildConfiguration)->makeCommand();
+    ToolChain *tc = toolChain(buildConfiguration);
+    return tc ? tc->makeCommand() : "make";
 }
 
 QString Qt4Project::defaultMakeTarget(const QString &buildConfiguration) const
 {
-    return toolChain(buildConfiguration)->defaultMakeTarget();
+    ToolChain *tc = toolChain(buildConfiguration);
+    return tc ? toolChain(buildConfiguration)->defaultMakeTarget() : "";
 }
 
 void Qt4Project::updateCodeModel()
@@ -740,7 +742,9 @@ ProjectExplorer::Environment Qt4Project::baseEnvironment(const QString &buildCon
 {
     Environment env = useSystemEnvironment(buildConfiguration) ? Environment::systemEnvironment() : Environment();
     qtVersion(buildConfiguration)->addToEnvironment(env);
-    toolChain(buildConfiguration)->addToEnvironment(env);
+    ToolChain *tc = toolChain(buildConfiguration);
+    if (tc)
+        tc->addToEnvironment(env);
     return env;
 }