Merge r1866760 from ^/httpd/apreq/trunk:

Merge r1866760 from ^/httpd/apreq/trunk:

parser_multipart: fix NULL pointer dereference in nested multipart

create_multipart_context() can return NULL if the given Content-Type
was not recognized (if there is no "boundary" attribute).  This
crashes libapreq2.

This bug was introduced by SVN commit 227276.  Prior to this commit,
there was a NULL check, but the commit removed it:

 http://svn.apache.org/viewvc/httpd/apreq/trunk/library/parser_multipart.c?r1=227276&r2=227275&pathrev=227276

Submitted by: max

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1867761 13f79535-47bb-0310-9956-ffa450edef68