Using a ltr context, I've created a layout with 3 rtl characters (hebrew 
from the 'ezra sil' font), so there are 6 bytes total.  I then ask for an 
iterator, and call pango_layout_iterator_next_char() on it, but the 
assertion in this function fails on the first call. 
 
Tracing through with gdb, I see that the iterator's ltr field is set to 
0, which is correct, but its index is also set to 0.  I think this is 
wrong, since the first glyph displayed is the 3rd in the text stream, so 
that the index ought to start out as 6.