fix: properly set location data in OUTDENT nodes

[alangpierce]

Backport of jashkenas#4291 .

In f609036, a line was changed from
if length > 0 then (length - 1) else 0 to Math.max 0, length - 1. However,
in some cases, the length variable can be undefined. The previous code would
correctly compute lastCharacter as 0, but the new code would compute it as
NaN. This would cause trouble later on: the end location would just be the end
of the current chunk, which would be incorrect.

Here's a specific case where the parser was behaving incorrectly:

a {
  b: ->
    return c d,
      if e
        f
}
g

The OUTDENT tokens after the f had an undefined length, so the NaN made it
so the end location was at the end of the file. That meant that various nodes in
the AST, like the return node, would incorrectly have an end location at the
end of the file.

To fix, I just reverted the change to that particular line.

Also add a test that tokens have locations that are in order