If sp--skip-match-p is called with closing delimiter the pair-skip defaults to nil

[Fuco1]

Expected behavior

The skip function should also be accessed by the closing delimiter, see sp-get-paired-expression lookup

This makes sp-get-thing's check broken if the first encountered delimiter is a closing one.

[Fuco1]

This might still be a potential problem if we do not search via sp-get-thing but sp-get-paired-expression where we also have some (shared?) logic to search for first valid pair.