Initialize sub_nodes glist in the root config node.

An empty config file will result in NULL sub_nodes list rather an an
empty sub_nodes list resulting in a segfault later.

Also added a check to make sure we don't add a NULL entry to sub_nodes
list when all blocks are empty.

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>
Acked-by: Frank S. Filz <ffilzlnx@mindspring.com>
Merge branch 'tp/lex-list' into ibm_next_2Xmerge_tmp