Catch the somewhat absurd combination of a 417 error where no Expect header

was present, on some platforms avoiding a segfault.

Backports: 814048, 814114
Reviewed by: wrowe, minfrin, covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@814723 13f79535-47bb-0310-9956-ffa450edef68