fix(frontends/lean/builtin_cmds): abort `eval` after error recovery and complain about unsynthesized mvars early
fix(frontends/lean/builtin_cmds): abort `eval` after error recovery and complain about unsynthesized mvars early

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