Windows builds fail when no version of Python is present

Bug report

When building python 3.11.0 on windows, if no version of python already exists, the build fails due to apparently malformed nuget commands.

       FindPythonForBuild:

         Downloading nuget...

         Feeds used:

           https://api.nuget.org/v3/index.json



         Installing package 'pythonx86' to 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals'.

           GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/index.json

           OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/index.json 123ms

           GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.5.2/3.8.1-c1.json

           GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.8.1/3.10.4.json

           GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.10.5/3.12.0-a1.json

           OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.8.1/3.10.4.json 33ms

           OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.5.2/3.8.1-c1.json 88ms

           OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.10.5/3.12.0-a1.json 94ms



         Attempting to gather dependency information for package 'pythonx86.3.11.0' with respect to project 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals', targeting 'Any,Version=v0.0'

         Gathering dependency information took 48 ms

         Attempting to resolve dependencies for package 'pythonx86.3.11.0' with DependencyBehavior 'Lowest'

         Resolving dependency information took 0 ms

         Resolving actions to install package 'pythonx86.3.11.0'

         Resolved actions to install package 'pythonx86.3.11.0'

         Retrieving package 'pythonx86 3.11.0' from 'nuget.org'.

           GET https://api.nuget.org/v3-flatcontainer/pythonx86/3.11.0/pythonx86.3.11.0.nupkg

           OK https://api.nuget.org/v3-flatcontainer/pythonx86/3.11.0/pythonx86.3.11.0.nupkg 62ms

         Installed pythonx86 3.11.0 from https://api.nuget.org/v3/index.json with content hash V5oJYri31E20HR7Z1EfzCiYObF8U6ECVIZ2Rg4BifoH31dRA48nQTOOP6ClcGpfrjK4yZOQrgB4HxoEQqMYmYA==.

         Adding package 'pythonx86.3.11.0' to folder 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals'

         Added package 'pythonx86.3.11.0' to folder 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals'

         Successfully installed 'pythonx86 3.11.0' to C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals

         Executing nuget actions took 7.4 sec

         "C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\PCbuild\\\\..\\externals\\pythonx86\\tools\\python.exe"

         Using PythonForBuild=Downloading nuget...;Feeds used:;https://api.nuget.org/v3/index.json;Installing package 'pythonx86' to 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals'.;GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/index.json;OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/index.json 123ms;GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.5.2/3.8.1-c1.json;GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.8.1/3.10.4.json;GET https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.10.5/3.12.0-a1.json;OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.8.1/3.10.4.json 33ms;OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.5.2/3.8.1-c1.json 88ms;OK https://api.nuget.org/v3/registration5-gz-semver2/pythonx86/page/3.10.5/3.12.0-a1.json 94ms;Attempting to gather dependency information for package 'pythonx86.3.11.0' with respect to project 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals', targeting 'Any,Version=v0.0';Gathering dependency information took 48 ms;Attempting to resolve dependencies for package 'pythonx86.3.11.0' with DependencyBehavior 'Lowest';Resolving dependency information took 0 ms;Resolving actions to install package 'pythonx86.3.11.0';Resolved actions to install package 'pythonx86.3.11.0';Retrieving package 'pythonx86 3.11.0' from 'nuget.org'.;GET https://api.nuget.org/v3-flatcontainer/pythonx86/3.11.0/pythonx86.3.11.0.nupkg;OK https://api.nuget.org/v3-flatcontainer/pythonx86/3.11.0/pythonx86.3.11.0.nupkg 62ms;Installed pythonx86 3.11.0 from https://api.nuget.org/v3/index.json with content hash V5oJYri31E20HR7Z1EfzCiYObF8U6ECVIZ2Rg4BifoH31dRA48nQTOOP6ClcGpfrjK4yZOQrgB4HxoEQqMYmYA==.;Adding package 'pythonx86.3.11.0' to folder 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals';Added package 'pythonx86.3.11.0' to folder 'C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals';Successfully installed 'pythonx86 3.11.0' to C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\externals;Executing nuget actions took 7.4 sec;"C:\\builds\\sources\\202db9a1-4e19-51e0-bc2f-be2b07ba07bb\\Python-3.11.0\\PCbuild\\\\..\\externals\\pythonx86\\tools\\python.exe"

Then, later:

         'Downloading' is not recognized as an internal or external command,

         operable program or batch file.

Review the PCbuild FindPythonForBuild step and the logged NuGet output first. Reproduce a Windows build with no pre-existing Python installation, then trace why the downloaded command output becomes the PythonForBuild value. Done means the build proceeds without treating 'Downloading' as a command.