gbookmarkfile: Fix error reporting with unexpected nesting of elements
The parser state machine for bookmark files did not handle unexpected nesting of elements, such as a element inside a element — it would print a critical warning rather than returning a GError.
Fix that, and add various unit tests for it. The set of tests includes various other general markup tests as provided by Jussi Judin.
Signed-off-by: Philip Withnall withnall@endlessm.com
Closes #1035 (closed)