Allow to get mime part from text part in lua.
Allow to get mime part from text part in lua.

awhitesong/rspamd,andrejzverev/rspamd,dark-al/rspamd,andrejzverev/rspamd,amohanta/rspamd,AlexeySa/rspamd,minaevmike/rspamd,minaevmike/rspamd,amohanta/rspamd,andrejzverev/rspamd,dark-al/rspamd,minaevmike/rspamd,minaevmike/rspamd,awhitesong/rspamd,AlexeySa/rspamd,AlexeySa/rspamd,dark-al/rspamd,dark-al/rspamd,amohanta/rspamd,minaevmike/rspamd,AlexeySa/rspamd,dark-al/rspamd,awhitesong/rspamd,amohanta/rspamd,andrejzverev/rspamd,AlexeySa/rspamd,awhitesong/rspamd,minaevmike/rspamd,amohanta/rspamd,andrejzverev/rspamd,minaevmike/rspamd,AlexeySa/rspamd,andrejzverev/rspamd,minaevmike/rspamd,andrejzverev/rspamd,AlexeySa/rspamd,minaevmike/rspamd,andrejzverev/rspamd,AlexeySa/rspamd,AlexeySa/rspamd