ocaml: catch special case when expression is just an identifier
ocaml: catch special case when expression is just an identifier

Improve type completion, prevent "Not_found" error to escape.

the-lambda-church/merlin,haselwarter/merlin,dra27/merlin,chriskonstad/merlin,the-lambda-church/merlin,neojski/merlin,the-lambda-church/merlin,rgrinberg/merlin,rgrinberg/merlin,ocaml/merlin,neojski/merlin,haselwarter/merlin,chambart/merlin,dra27/merlin,fxfactorial/merlin,haselwarter/merlin,haselwarter/merlin,rgrinberg/merlin,chambart/merlin,ocaml/merlin,fxfactorial/merlin,ocaml/merlin,fxfactorial/merlin,chambart/merlin,chriskonstad/merlin,ocaml/merlin,chambart/merlin,dra27/merlin,rgrinberg/merlin,neojski/merlin,fxfactorial/merlin,neojski/merlin,dra27/merlin