fix(frontends/lean/server): crash: uninitialized memory
fix(frontends/lean/server): crash: uninitialized memory

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

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