Fixed full comment parsing in AST converter.

src/Core/Parser/ASTConverter.cs

@@ -640,10 +640,12 @@ namespace CppSharp
                 Kind = ConvertRawCommentKind(rawComment.RawCommentKind),
                 BriefText = rawComment.BriefText,
                 Text = rawComment.Text,
-                FullComment = commentConverter.Visit(rawComment.FullComment)
-                    as AST.FullComment
             };
 
+            if (rawComment.FullComment != null)
+                _rawComment.FullComment = commentConverter.Visit(rawComment.FullComment)
+                    as AST.FullComment;
+
             return _rawComment;
         }