Add test for multiple invalid xpath expressions in a row.
Add test for multiple invalid xpath expressions in a row.

sferik/libxml-ruby,sferik/libxml-ruby,xml4r/libxml-ruby,increments/libxml-ruby,increments/libxml-ruby,xml4r/libxml-ruby,increments/libxml-ruby,xml4r/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby