[mod_nss] avoid NSS crash w/ config file error
[mod_nss] avoid NSS crash w/ config file error

NSS crashes with SIGFPE if SSL_REQUEST_CERTIFICATE is PR_TRUE,
but trust anchors have not been set with SSL_SetTrustAnchors()
(e.g. if ssl.verifyclient.activate = "enable" but ssl.ca-file
      has not been configured in lighttpd.conf)

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4