temp file gets deleted, handle case


Logs:
```
System. TypeInitializationException : The type initializer for
'IntelliTect.Multitool.RepositoryPaths' threw an exception.
System. IO. FileNotFoundException : Could not find file 'C: \U
\IntelliTect.MultiTool.BuildVariables.tmp'.

This exception was originally thrown at this call stack:
Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile(string, System.IO.FileMode, System.IO.FileAccess, System.IO.FileShare, System.IO.FileOptions)
Microsoft.Win32.SafeHandles.SafeFileHandle.Open(string, System.IO.FileMode, System.IO.FileAccess, System.IO.FileShare, System.IO.FileOptions, long, System.IO.UnixFileMode?)
System.IO.Strategies.OSFileStreamStrategy.OSFileStreamStrategy(string, System.IO.FileMode, System.IO.FileAccess, System.IO.FileShare, System.IO.FileOptions, long, System.IO.UnixFileMode?)
System.IO.Strategies.FileStreamHelpers.ChooseStrategyCore(string, System.IO.FileMode, System.IO.FileAccess, System.IO.FileShare, System.IO.FileOptions, long, System.IO.UnixFileMode?)
System.IO.StreamReader.ValidateArgsAndOpenPath(string, System.Text.Encoding, int)
System.IO.File.ReadAllLines(string, System.Text.Encoding)
IntelliTect.Multitool.RepositoryPaths.RepositoryPaths()
```

Possible repro steps:

- Project sat idle for a week or two without any work on it, project remained closed
- various Windows stuff happened that ultimately purged that temp file
- I open the project back up and run the tests, function doesn't work anymore

Investigate if the file isn't there as expected, handling that case.