Be more defensive in the parser translator lexer

[Earlopain]

Fixes rubocop/rubocop#14100
Fixes #3550

Generally I have been good about safely accessing the tokens but failed to properly guard against no tokens in places
where it could theoretically happen through invalid syntax.

I added a test case for one occurance, other changes are theoretical only.

Also, TIL that this works:

a = [[1,2], [3,4]]
i = 0

while (foo, _ = a[i])
  puts foo
  i += 1
end
# => 1
# => 3

I make use of that construct to safely access the data without much changes. Makes some code easier actually.