Fix source file check for non portable pdb

[MarcoRossignoli]

Thank's to @adrianhara #524 (comment) I found an issue on new local source file check during instrumentation.
If pdf is not a portable pdb metadataReaderProvider.GetMetadataReader() throws exception Invalid COR20 header signature. because we can read only portable pdb.

For now in case of exception for this reason we'll skip check so we'll instument module.
Return false would block user and in case of issue we'll can skip bad module with exclusion filter, so I think it's a good solution.

cc: @tonerdo @petli

Thank's a lot Adrian for the repro!

NB: minor change, I fixed redundant verbosity log.
New verbose output

[MarcoRossignoli]

@adrianhara could be great if tomorrow you'll give it a try(with nightly) with non portable pdb and tell us if it works as expected!

[adrianhara]

@MarcoRossignoli thanks for the quick fix. I'll give it a try and let you know.

[adrianhara]

I tried the latest nightly and it works fine. Thanks @MarcoRossignoli ! 👍

[MarcoRossignoli]

@adrianhara we released new package https://www.nuget.org/packages/coverlet.msbuild/2.7.0 you can switch to production!