Misleading syntax error for malformed local names after prefixes

[mkroetzsch]

Consider the following malformed program:

@prefix wd: <http://www.wikidata.org/entity/> .
in(1,wd:Q42,2).
test1(?x) :- in(1, wd:42, 2).

The term wd:42 is illegal, since local names cannot start with a number. However, Nemo shows an error for the previous occurrence of the predicate in, and the error message is

expected '.'

It would be good if the parser could pinpoint the real problem more accurately, since it is a common typo.

[mmarx]

This is related to #624.