fix(frontends/lean/parser): uninitialized var error reported by valgrind
fix(frontends/lean/parser): uninitialized var error reported by valgrind

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

c-cube/lean,fpvandoorn/lean,soonhokong/lean,johoelzl/lean,rlewis1988/lean,avigad/lean,Kha/lean,dselsam/lean,leodemoura/lean,eigengrau/lean,sp3ctum/lean,eigengrau/lean,rlewis1988/lean,c-cube/lean,soonhokong/lean-osx,fgdorais/lean,UlrikBuchholtz/lean,eigengrau/lean,leodemoura/lean,soonhokong/travis_test,fgdorais/lean,c-cube/lean,soonhokong/lean-osx,Kha/lean,htzh/lean,fpvandoorn/lean,leodemoura/lean,Kha/lean,digama0/lean,levnach/lean,codyroux/lean0.1,leanprover-community/lean,htzh/lean,avigad/lean,codyroux/lean0.1,rlewis1988/lean,avigad/lean,fgdorais/lean,Kha/lean,soonhokong/lean-windows,leanprover/lean,sp3ctum/lean,leanprover-community/lean,soonhokong/lean-osx,javra/lean,digama0/lean,fpvandoorn/lean,rlewis1988/lean,digama0/lean,levnach/lean,Kha/lean,fpvandoorn/lean,levnach/lean,fpvandoorn/lean,leanprover-community/lean,soonhokong/lean,leanprover-community/lean,UlrikBuchholtz/lean,leanprover/lean,dselsam/lean,johoelzl/lean,UlrikBuchholtz/lean,fgdorais/lean,soonhokong/lean,avigad/lean,fpvandoorn/lean2,UlrikBuchholtz/lean,levnach/lean,leodemoura/lean,rlewis1988/lean,leanprover/lean,leanprover/lean,digama0/lean,javra/lean,codyroux/lean0.1,digama0/lean,c-cube/lean,soonhokong/travis_test,leodemoura/lean,fpvandoorn/lean2,htzh/lean,avigad/lean,Kha/lean,soonhokong/lean,dselsam/lean,htzh/lean,soonhokong/lean,fpvandoorn/lean2,leodemoura/lean,fpvandoorn/lean2,leanprover/lean,fgdorais/lean,leanprover-community/lean,digama0/lean,soonhokong/travis_test,javra/lean,UlrikBuchholtz/lean,dselsam/lean,soonhokong/travis_test,javra/lean,dselsam/lean,leanprover/lean,soonhokong/lean-windows,johoelzl/lean,soonhokong/lean-osx,soonhokong/lean-windows,soonhokong/lean-osx,levnach/lean,codyroux/lean0.1,johoelzl/lean,c-cube/lean,sp3ctum/lean,johoelzl/lean,soonhokong/lean-windows,soonhokong/lean-windows,fpvandoorn/lean2,avigad/lean,johoelzl/lean,fgdorais/lean,fpvandoorn/lean,javra/lean,eigengrau/lean,sp3ctum/lean,dselsam/lean,eigengrau/lean,htzh/lean,leanprover-community/lean,sp3ctum/lean,rlewis1988/lean