max in httpd

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:

apreq_brigade_move() bugfix: pass previous bucket to APR_RING_x()