trig: stack overflow when there is an excess of prefixes

[tpluscode]

Try this snippet: https://runkit.com/embed/5xvu3rhd5z0u

Python's rdflib extract a buttload of prefixes out of virtually any URI it comes across.

Graphy does not like it and fails with

RangeError: Maximum call stack size exceeded
at RegExp.exec in ECMAScript
at match_prefixed_name_escapeless in @graphy/content.trig.read/main.js — line 302
at Reader.match_prefixed_name_escapeless in @graphy/content.trig.read/main.js — line 588
at Reader.block (as _f_state) in @graphy/content.trig.read/main.js — line 1491
at Reader.full_stop in @graphy/content.trig.read/main.js — line 4486
at Reader.prefix_iri in @graphy/content.trig.read/main.js — line 4342