merge_atlases does not remove overlapping regions

[yonestar]

If two atlas being merged contain an overlapping set of regions, the merged atlas contains double copies of this region.

Toy example that reproduces the bug:

atlas_obj = load_atlas('canlab2018_2mm');
amy = select_atlas_subset(atlas_obj, {'Amy'})
double_amy = merge_atlases(amy, amy)

% check result
double_amy.labels

ans =

  1×8 cell array

    {'Amygdala_CM_'}    {'Amygdala_SF_'}    {'Amygdala_AStr_'}    {'Amygdala_LB_'}    {'Amygdala_CM_'}    {'Amygdala_SF_'}    {'Amygdala_AStr_'}    {'Amygdala_LB_'}

The 'always_replace' and the 'noreplace' options to merge_atlases do not address this.

I hesitate to try and fix because there already seems to be a complex logic regarding the 'always_replace' and the 'noreplace' options, and I am unsure how this would intersect with the issue reported here.