Turtle serializer : no whitespace between colon and dot when a prefixed symbol has no local name

[pduchesne]

If a prefixed symbol is a statement's object and has no local name, it results in a colon immediately followed by a dot, e.g. example:subject example:pred example:.
In particular, the automatic prefix production of the turtle serializer produces such outputs if a symbol has a trailing slash.

While this is syntactically valid as per the turtle grammar, some other tools do not handle this well (e.g. RDFLib/rdflib , cf RDFLib/rdflib#1664) and require a whitespace between the colon and the dot.
In the sake of cross-ecosystems interoperability, fixing this would be an easy win.