ap_rgetline_core: fix a bug with folding observed while testing ebcdic.

ap_rgetline_core: fix a bug with folding observed while testing ebcdic.
Garbage characters sometimes appeared after a legitimate folded header.
We weren't allocating an extra byte for the trailing null, or copying it,
when called from get_mime_headers (folding is in use, and ap_rgetline is
responsible for allocating memory).  No need to worry about a trailing
LF - it's already been nuked.

I checked the partial line code to see if it had a similar bug.  It looked
like it did, and that the code which trims the back end of the line would
run multiple times and whack innocent bytes.  However, gdb showed that this
section of code appears to be dead due to input filter chain changes.

also, removed an assignment to a dead variable.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93804 13f79535-47bb-0310-9956-ffa450edef68