prefixed URIs with forward slash not rendered correctly

[gramian]

When a forward slash (escaped with a reserved character escape sequences) is part of a prefixed URI, for example:

doi:10.0000\/foobar

it is rendered as nsX:foobar with X a number. Replacing \/' i.e. by _` leads to a correct rendering.

Discovered using the fork https://github.com/fatestigma/ontology-visualization on Ubuntu 20.04, with Python 3.8.10, and python3-rdflib 4.2.2-5.