Do explicit zero-length checking for certain HTTP requests that break Pa...

...ssenger.

While testing Spirit I noticed that renaming scripts was failing in DS Admin. In order to troubleshoot I ran the site with rackup and had no issues. Fast-forward past 2 hours of packet sniffing and debug trace reading when I  figured out that the POST request for the rename (/scripts/ren) is being sent as text/xml with a zero content_length which triggers processing by CFPropertyList. This fails with NilClass errors, because there's nothing to parse. I suspect that WeBRick processes the POST request with zero length by not passing content_length while Passenger does, thus triggering the XML parsing with CFPropertyList of nil content.

Anyway. Changing the check from simply "content_length exists" to "content_length is not zero length" seems to successfully skip over the XML parsing.