Avoid allocating checking extension (#2574)
Avoid allocating checking extension (#2574)

IsVCProjFilename was allocating 0.1% in a large solution's evaluation.
mono/msbuild,mono/msbuild,mono/msbuild,chipitsine/msbuild,chipitsine/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,chipitsine/msbuild,Microsoft/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,jeffkl/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,cdmihai/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,cdmihai/msbuild,chipitsine/msbuild,Microsoft/msbuild,Microsoft/msbuild,Microsoft/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild,mono/msbuild,AndyGerlicher/msbuild