TrigEgammaAnalysisTools: Fix property initialization ordering problem

TrigEgammaAnalysisBaseTool holds a plotting tool, m_plot. It also has a property doEmulation, and it sets up a callback on this property so that when it it set, it is propagated to the subordinate tools, including m_plot. However, if the JO service ends up setting the doEmulation property before the PlotTool property, then m_plot will not be valid in the callback, leading to errors from ToolSvc.

To fix this, check that m_plot is valid in the callback, and further arrange to call the call back in initialize().