imap-send: only use CURLOPT_LOGIN_OPTIONS if it is actually available
imap-send: only use CURLOPT_LOGIN_OPTIONS if it is actually available

This fixes the compilation on an older Linux that was used to debug
test failures when upgrading Git for Windows to Git v2.3.0.

Signed-off-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git