Fix bug where add script file command is not enabled correctly.
Fix bug where add script file command is not enabled correctly.

dsplaisted/NuGetPackageExplorer,campersau/NuGetPackageExplorer,NuGetPackageExplorer/NuGetPackageExplorer,NuGetPackageExplorer/NuGetPackageExplorer,BreeeZe/NuGetPackageExplorer