Make it more robust against a spoofed filename

[mame]

Currently, RubyVM::AST.of attempts to reopen a file based on iseq's file
path. However, it opens a wrong file if the iseq's file path is spoofed.

module Dummy
  binding.irb
end

$ ruby test.rb

From: test.rb @ line 2 :

    1: module Dummy
 => 2:   binding.irb
    3: end

irb(Dummy):001:0> foo
/home/mame/work/ruby/local/lib/ruby/3.1.0/error_highlight/base.rb:412:in `spot_colon2': undefined method `last_lineno' for nil:NilClass (NoMethodError)

      if nd_parent.last_lineno == @node.last_lineno
                  ^^^^^^^^^^^^

Found by @kateinoigakukun

Though this is a fundamental design issue of RubyVM::AST.of,
in any way it would be good to make error_highlight robust for
unexpected exception.

In a long term, this particular issue would be fixed by adding to irb an
option RubyVM::ISeq.keep_script_lines = true (which is not implemented
yet).

[mame]

This issue was fixed in the side of the interpreter. I just merge the test.

Just for record: Maybe this issue is related to #16.