[RCU] upgrade to php 7.3

Hello!

Today I upgraded from php 5.x to php 7.3 and removed php 5.x completly. Now I found I get a blank screen calling roundcube.

I then added error_reporting(E_ALL); ini_set('display_errors', 'On');

and get Notice: Undefined index: env in /usr/share/roundcubemail/index.php on line 46 Notice: Undefined variable: rcmail_config in /usr/share/roundcubemail/program/lib/Roundcube/rcube_config.php on line 325 Notice: Undefined offset: 2 in /usr/share/roundcubemail/program/lib/Roundcube/rcube_charset.php on line 223

Is there a way to fix this? Should I install roundcube form scratch?