FIX : fix the read_annot when parcellation has missing values and orig_ids=False.
Vertices with 0 label were randomly merged with the first entry in the colortable
Merge pull request #194 from agramfort/fix_read_annotation

MRG : ugly hack to fix the read_annot when parcellation has missing values

The issue comes with annot that have missing values ie that don't cover the entire cortex.