Fixes a bug with arithmetic's new attempt solution infrastructure. This caused arith...

Fixes a bug with arithmetic's new attempt solution infrastructure.  This caused arithmetic to think it was in a conflict incorrectly. This lead to it not properly responding to new input and lead to an inconsistency bug.

This could be triggered previously by running:
./builds/bin/cvc4 --stats --no-restrict-pivots --enable-miplib-trick --miplib-trick-subs=2 --fc-penalties --collect-pivot-stats --new-prop --dio-decomps --unconstrained-simp --fancy-final /home/taking/benchmarks/smtlib2/QF_LRA/miplib/opt1217--17.smt2