bpo-30450: Adds alternate download approach for nuget.exe (#2737)

* bpo-30450: Adds alternate download approach for nuget.exe

* Whitespace fix.
diff --git a/PCbuild/find_python.bat b/PCbuild/find_python.bat
index 4629c61..82358c8 100644
--- a/PCbuild/find_python.bat
+++ b/PCbuild/find_python.bat
@@ -42,7 +42,8 @@
     @echo Downloading nuget...
     @rem NB: Must use single quotes around NUGET here, NOT double!
     @rem Otherwise, a space in the path would break things
-    @powershell.exe -Command Invoke-WebRequest %_Py_NUGET_URL% -OutFile '%_Py_NUGET%'
+    @rem If it fails, retry with any available copy of Python
+    @powershell.exe -Command Invoke-WebRequest %_Py_NUGET_URL% -OutFile '%_Py_NUGET%' || @py -c "%~dp0\urlretrieve.py" "%_Py_NUGET_URL%" "%_Py_NUGET%"
 )
 @echo Installing Python via nuget...
 @"%_Py_NUGET%" install pythonx86 -ExcludeVersion -OutputDirectory "%_Py_EXTERNALS_DIR%"