uribl: fix for CRIT (see below)

Aug 31 11:23:17 filter1-mail haraka[73661]: [CRIT]
[7B9E9C9A-D4B7-492E-B32D-3D0C116CF333.1] [core] Plugin data.uribl failed:
TypeError: Cannot read property 'bodytext' of null     at extract_urls
(/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:350:40)     at
do_body (/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:327:9)
at chain_caller
(/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:340:9)     at
do_msgid_header
(/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:321:9)     at
chain_caller (/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:340:9)
at do_replyto_header
(/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:311:9)     at
chain_caller (/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:340:9)
at do_from_header
(/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:301:9)     at
chain_caller (/usr/local/lib/node_modules/Haraka/plugins/data.uribl.js:340:9)
at Plugin.exports.hook_data_post
(/usr/local/lib/node_modules/Haraka/plugins/data.