fixed: Project.GetReferencedProjects raises NRE during VS closing
fixed: Project.GetReferencedProjects raises NRE during VS closing

bleis-tift/FSharpVSPowerTools,enricosada/VisualFSharpPowerTools,dkinitiate/VisualFSharpPowerTools,vasily-kirichenko/FSharpVSPowerTools,forki/FSharpVSPowerTools,ovatsus/VisualFSharpPowerTools,smoothdeveloper/VisualFSharpPowerTools,bleis-tift/FSharpVSPowerTools,bentayloruk/FSharpVSPowerTools,dungpa/PowerTools,cloudRoutine/VisualFSharpPowerTools,xperiandri/VisualFSharpPowerTools,fsprojects/VisualFSharpPowerTools,0x53A/VisualFSharpPowerTools,enricosada/VisualFSharpPowerTools,dedale/VisualFSharpPowerTools,fsprojects/VisualFSharpPowerTools,cloudRoutine/VisualFSharpPowerTools,yever/VisualFSharpPowerTools,isaacabraham/VisualFSharpPowerTools,vasily-kirichenko/FSharpVSPowerTools