Illegal access crash from if-modified-since header

[ghost]

node inherits a bug from v8 where some dates raise exceptions instead of returning an Invalid Date object:

$ node
> new Date('275760-09-12')
Fri Sep 12 275760 00:00:00 GMT-0400 (EDT)
> new Date('275760-09-13')
Invalid Date
> new Date('275760-09-23')
Invalid Date
> new Date('275760-09-24')
illegal access
> new Date('275760-10-13')
illegal access
> new Date('275760-10-14')
Invalid Date
> ^D
$ node -v
v4.2.1

Knowing this, it's possible to crash ecstatic by sending a malicious If-Modified-Since header:

$ mkdir /tmp/xyz
$ echo '<h1>doot doot</h1>' > /tmp/xyz/index.html
$ ecstatic -p 5000 /tmp/xyz &
[1] 11994
$ curl -H if-modified-since:275760-09-24 http://localhost:5000/index.html

/home/substack/projects/node-ecstatic/lib/ecstatic.js:280
      if (modifiedSince && (new Date(Date.parse(modifiedSince))) < stat.mtime) {
                                          ^
illegal access
curl: (52) Empty reply from server
[1]+  Exit 1                  ecstatic -p 5000 /tmp/xyz

This patch guards the Date instance with a try/catch to prevent these v8 bugs from bringing down ecstatic.

[ghost]

I submitted this bug upstream to v8: https://bugs.chromium.org/p/v8/issues/detail?id=4640