http://svn.apache.org/viewvc?view=rev&revision=535617
* Prevent a segmentation fault if one of the Cache-Control headers
s-maxage, max-age, min-fresh, max-stale has no value assigned.
In this case ignore s-maxage, max-age, min-fresh. For max-stale
it is valid to set no value. In this case set max-stale to 1 year
to signal that the client is accepting a stale response of any age.
This could be a DoS if a threaded MPM and mod_cache is used.