Pipeline Tool crashes if you add Content.mcgb fitself as a resource.

[Martenfur]

What version of MonoGame does the bug occur on:

• MonoGame 3.8 latest dev build

What operating system are you using:

• Windows 10 64x

What MonoGame platform are you using:

• DesktopGL

If you add Content.mgcb as a resource, e.g:

#begin Content.mgcb
/importer:AssetInfoImporter
/processor:PassThroughProcessor
/build:Content.mgcb

then close Pipeline Tool and then will try to open the content file again, pipeline tool will fail to open it and say that unknown error has occured.

If you try to build project with that content file, the build will fail and the output will show this:

Unhandled Exception: System.NotSupportedException: The given path's format is not supported.
2>     at System.Security.Permissions.FileIOPermission.EmulateFileIOPermissionChecks(String fullPath)
2>     at System.Security.Permissions.FileIOPermission.QuickDemand(FileIOPermissionAccess access, String fullPath, Boolean checkForDuplicates, Boolean needFullPath)
2>     at MGCB.MGBuildParser.ParsePreprocessArg(String arg, List`1 output, Stack`1 ifstack, Boolean inResponseFile)
2>     at MGCB.MGBuildParser.ParsePreprocessArg(String arg, List`1 output, Stack`1 ifstack, Boolean inResponseFile)
2>     at MGCB.MGBuildParser.Preprocess(IEnumerable`1 args)
2>     at MGCB.MGBuildParser.Parse(IEnumerable`1 args)
2>     at MGCB.Program.Main(String[] args)

The same setup works correctly on MG 3.7.1.