PHP 8 warning in managesieve plugin when more than one action is configured for a rule

[javier-angulo]

When adding an additional action to a rule in managesieve, a php 8 warning is logged:

 PHP Deprecated:  strip_tags(): Passing null to parameter #1 ($string) of type string is deprecated in /usr/share/roundcubemail/plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php on line 2780

If 3 actions are configured, 2 warnings are logged and so on.

[alecpl]

Fixed.