[LG] Fix missing trailing line break with String.Readline()

[Danieladu]

In C#, LG use StringReader.ReadLine to read the content line from LG file, but there may exist some points that do not match the LG's requirements.

In C# doc: https://docs.microsoft.com/en-us/dotnet/api/system.io.stringreader.readline?view=netframework-4.8#remarks

The string that is returned does not contain the terminating carriage return or line feed. The returned value is null if the end-of-stream marker has been reached. That is to say, if there is nothing between the last line read and the end-of-stream marker, the method returns null.

So, the trailing newlines would be dropped when parsing the text with ReadLine method.

if the template is:

# template
- hi

and do some CRUD operation on this template, finally, we would get the template body:

- hi

the tailing newlines are missing.