#12 Check that synconcealed() changes don't break anything

[Anonymous]

Originally created by: fritzophrenic

Original report by Ben Fritz (Bitbucket: fritzophrenic NA, ).

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This commit changes the behavior of synconcealed(), I need to double-check if that causes problems for consecutive concealed regions:

https://github.com/vim/vim/commit/cc0750dc6e878394ab0fd922b7ea4280918ae406