Import of Excel fails if the neutral resource file have been deleted

**Describe the bug**
Resx Manager fails to import all translations when the neutral resource file have been deleted, but there still is a localized version.

* ~~MyResource.resx~~
* MyResource.da.resx

**To Reproduce**
1. Create a resource file with a single row
2. Translate the row to another language
3. Export an Excel file of all rows
4. Delete the neutral resx file
5. Import the Excel file

**Expected behavior**
I would expect the ResxManager to skip importing the translation, similar to how it works if all the Resource files are deleted.

I tried debugging this a bit, but I was unable to detect where I would need to make my changes.
But I believe the primary culprit is here: https://github.com/dotnet/ResXResourceManager/blob/647beb330ccb12f7283fb73b2fe29acf8d3c0c68/src/ResXManager.Model/ResourceEntityExtensions.cs#L204-L218