Prevent invalid xml output of null characters

Prevent the xml renderer from throwing a 500 internal server error:

ActionView::Template::Error (string contains null byte)

Co-authored-by: Victor Pereira <vpereira@suse.com>

src/api/app/models/comment.rb

@@ -69,6 +69,7 @@ def to_xml(builder, include_commentable = false)
       attrs['project'] = commentable.project if commentable.is_a?(Package)
     end
     attrs[:parent] = parent_id if parent_id
+    body.delete!("\u0000")
 
     builder.comment_(attrs) do
       builder.text(body)