Update UnParserExtensions.cs

If there is no long name, take the short name regardless of the preference setting

Author: gbritton1

src/CommandLine/UnParserExtensions.cs

@@ -206,8 +206,10 @@ private static string FormatOption(OptionSpecification spec, object value, UnPar
 
         private static string FormatName(this OptionSpecification optionSpec, UnParserSettings settings)
         {
-            // Short name not preferred? Go with long! No short name? Has to be long!
-            var longName = !settings.PreferShortName || optionSpec.ShortName.Length == 0;
+            // Have a long name and short name not preferred? Go with long! 
+            // No short name? Has to be long!
+            var longName = (optionSpec.LongName.Length >  0 && !settings.PreferShortName)
+                         || optionSpec.ShortName.Length == 0;
 
             return
                 new StringBuilder(longName