fix(frontends/lean/elaborator): fix segfault
fix(frontends/lean/elaborator): fix segfault

leanprover/lean,johoelzl/lean,dselsam/lean,fpvandoorn/lean,rlewis1988/lean,rlewis1988/lean,leanprover/lean,dselsam/lean,digama0/lean,fpvandoorn/lean,avigad/lean,leodemoura/lean,digama0/lean,Kha/lean,leanprover-community/lean,fpvandoorn/lean,avigad/lean,Kha/lean,avigad/lean,Kha/lean,avigad/lean,leodemoura/lean,digama0/lean,rlewis1988/lean,leanprover/lean,leodemoura/lean,johoelzl/lean,rlewis1988/lean,leanprover/lean,johoelzl/lean,dselsam/lean,leanprover-community/lean,johoelzl/lean,leanprover/lean,leodemoura/lean,leanprover/lean,avigad/lean,Kha/lean,digama0/lean,fpvandoorn/lean,leanprover-community/lean,Kha/lean,leanprover-community/lean,dselsam/lean,rlewis1988/lean,leodemoura/lean,Kha/lean,dselsam/lean,digama0/lean,leanprover-community/lean,johoelzl/lean,rlewis1988/lean,fpvandoorn/lean,johoelzl/lean,leodemoura/lean,digama0/lean,avigad/lean,fpvandoorn/lean,dselsam/lean,leanprover-community/lean