Lowering of invalid `.` Expr loops forever

[xal-0]

A . Expr with the wrong number of arguments causes lowering to get stuck, looping forever in flisp:

Meta.lower(Main, Expr(:., :a, :b, :c))

This doesn't usually come up in practice, but was revealed while fuzzing new REPL code. It can be produced if one converts the output of JuliaSyntax in ignore_errors mode:

julia> Expr(parsestmt(SyntaxNode, "a .b", ignore_errors=true))
:($(Expr(:., :a, :($(Expr(:error))), :(:b))))