Prevent NullReferenceException for null analysis type.

[hubuk]

PR Summary

Many analysis objects here have null Type field value. Not sure whether this is expected. Probably the Undetermined Type should be used instead of null. Anyway, similar precaution means are used in:

PSScriptAnalyzer/Engine/Helper.cs

Line 1059 in af02e80

psClass = classes.FirstOrDefault(item => String.Equals(item.Name, details.Type?.FullName, StringComparison.OrdinalIgnoreCase));

Creating test for this problem may be hard as the exception is not always being thrown.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
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[bergmeister]

Most of this code was forked from PowerShell's SMA codebase many years ago and not been touched much since. If you've seen an exception coming from this, such a tweak is OK I think and regression risk is small