Do not insert nested pair if we are using existng sexp's opener as prefix.

[Fuco1]

Expected behavior

Nothing should happen and the rest of the pair should probably get removed OR the closing pair should transform to match the opener instead of the closer being inserted right there.

Actual behavior

The closing delimiter is inserted right after point which makes the buffer imbalanced.

Steps to reproduce the problem

Try a tuareg-mode buffer with content (foo) and local pair

(sp-with-modes '(tuareg-mode) (sp-local-pair "(*" "*)" ))

Place the point before foo and hit *. The buffer breaks.