check_pipeline: use AP_MODE_SPECULATIVE to check for data in the input filters

check_pipeline:  use AP_MODE_SPECULATIVE to check for data in the input filters
to accomodate mod_ssl's input filter.  AP_MODE_EATCRLF is essentially a no-op
in that filter.

this fixes missing imbedded graphics etc when using the Event MPM with mod_ssl
with HTTP pipelining enabled in the browser.  the pipelined requests after the
first were never read from mod_ssl's input filter.  it might reduce unneeded
flushes with other MPMs.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@533820 13f79535-47bb-0310-9956-ffa450edef68