fix: properly set location data in OUTDENT nodes (jashkenas#2)

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

Author: alangpierce

lib/coffee-script/lexer.js

@@ -649,7 +649,7 @@ exports.Lexer = class Lexer
 
     # Use length - 1 for the final offset - we're supplying the last_line and the last_column,
     # so if last_column == first_column, then we're looking at a character of length 1.
-    lastCharacter = Math.max 0, length - 1
+    lastCharacter = if length > 0 then (length - 1) else 0
     [locationData.last_line, locationData.last_column] =
       @getLineAndColumnFromChunk offsetInChunk + lastCharacter
 

src/lexer.coffee

@@ -450,6 +450,25 @@ test "#3621: Multiline regex and manual `Regex` call with interpolation should
       eq tokenA.origin?[1], tokenB.origin?[1]
     eq tokenA.stringEnd, tokenB.stringEnd
 
+test "Verify tokens have locations that are in order", ->
+  source = '''
+    a {
+      b: ->
+        return c d,
+          if e
+            f
+    }
+    g
+  '''
+  tokens = CoffeeScript.tokens source
+  lastToken = null
+  for token in tokens
+    if lastToken
+      ok token[2].first_line >= lastToken[2].last_line
+      if token[2].first_line == lastToken[2].last_line
+        ok token[2].first_column >= lastToken[2].last_column
+    lastToken = token
+
 test "Verify all tokens get a location", ->
   doesNotThrow ->
     tokens = CoffeeScript.tokens testScript