Fix issues reported by Sonarqube and warnings reported by the compiler

.gitlab-ci.yml

plugins/Distribution/Distribution.cpp

plugins/MatrixVisualizer/Parsers/Parser.hpp

plugins/MatrixVisualizer/Windows/MatrixGLWidget.hpp

src/common/Session.cpp

src/common/Tools.cpp

src/core/Core.cpp

src/interface/Settings_window.cpp

src/main.cpp

src/parser/OTF2Parser/ParserDefinitionOTF2.cpp

src/parser/OTF2Parser/ParserDefinitionOTF2.hpp

src/parser/OTF2Parser/ParserEventOTF2.cpp

src/parser/OTFParser/mt_ParserOTF.cpp

src/parser/PajeParser/ParserDefinitionPaje.cpp

src/parser/PajeParser/ParserEventPaje.cpp

src/parser/PajeParser/mt_ParserEventPaje.cpp

src/parser/PajeParser/mt_ParserPaje.cpp

src/parser/ParsingThread.cpp

src/render/GanttDiagram.hpp

src/render/Render_alternate.cpp