CMake: Break loop in error handling

Block access to the BuildDirManager while one of its errors is
processed. This prevents more errors being raised as part of
error handling, which can trigger a loop.

Task-number: QTCREATORBUG-17869
Change-Id: Ic6f8d9a3c3b4e63f27260c40f27ab09d20b62b3e
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/cmakeprojectmanager/builddirmanager.h

@@ -86,6 +86,7 @@ signals:
 
 private:
     void emitDataAvailable();
+    void emitErrorOccured(const QString &message) const;
     void checkConfiguration();
 
     const Utils::FileName workDirectory() const;
@@ -109,6 +110,7 @@ private:
     std::unique_ptr<BuildDirReader> m_reader;
 
     mutable QList<CMakeBuildTarget> m_buildTargets;
+    mutable bool m_isHandlingError = false;
 };
 
 } // namespace Internal