data parser BUGFIX handle retturn code of lyxml_parse_mem()
data parser BUGFIX handle retturn code of lyxml_parse_mem()

detect error (not just empty data, real error) in XML parser and return
immediately

Fixes #21

PavolVican/libyang,lukasmacko/libyang,PavolVican/libyang,PavolVican/libyang,lukasmacko/libyang,PavolVican/libyang,PavolVican/libyang