Check if directory NLog.dll is detected in actually exists

[gregmac]

Fixes crash when an assembly location is found that doesn't actually exist.

I believe this happens when using in-memory or bundling loading of the library, as described at #736 (comment).

[304NotModified]

Thanks for this PR. It's a bit strange that this can happen, but no problem to check it first.

The change is in a good direction, bit I think it wise to:

• write another warning to the InternalLogger in this case
• check related code, like auto loading the xmlconfig (inside xmlloggingconfiguration)

[gregmac]

@304NotModified I updated with a separate log message. I was originally going to do that but didn't really have a good idea of what log message to use, hopefully 'not found' is appropriate?

I'm not sure what should be updated in XmlLoggingConfiguration (though I'm also not familiar with this codebase, other than as a user). All the file operations I see are a result of explicit configuration inside a config file -- so if a user specifies an include path that doesn't exist in a config file, I don't think this change should modify the current behaviour.

[codecov-io]

Current coverage is 75.43%

Merging #1432 into master will decrease coverage by -<.01%

@@             master      #1432   diff @@
==========================================
  Files           267        267          
  Lines         15993      15997     +4   
  Methods           0          0          
  Messages          0          0          
  Branches       1724       1725     +1   
==========================================
  Hits          12067      12067          
- Misses         3517       3520     +3   
- Partials        409        410     +1   

Powered by Codecov. Last updated by 04944f6...4faa313

[304NotModified]

Thanks!

[304NotModified]

I checked other places, and those are also OK.

This will be released next minor version. I have changed the log message so also the assemblyLocation will be printed.