Fix bug with charset conversion.
Fix bug with charset conversion.

Glib iconv understands only uppercase for charset names.

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