Fix for #43 breaks negation

[mmarx]

Consider the following edb.conf:

EDB0_predname=p
EDB0_type=INMEMORY
EDB0_param0=.
EDB0_param1=p
EDB1_predname=q
EDB1_type=INMEMORY
EDB1_param0=.
EDB1_param1=q

with p.csv containing

c

and q.csv containing

d

(i.e., both EDB predicates have a single constant fact).

Then the following rule

r(X) :- p(X),~q(X)

derives r(c) in 1b5dbdb (as expected), but r(d) in cf5a0ec and e0602fb, which is clearly wrong.

[CerielJacobs]

Fixed. Sorry about that, apparently I missed a case.

[mmarx]

No worries, thanks for the quick fix!