Fix PHP8 warnings

plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php

@@ -3239,7 +3239,7 @@ class rcube_sieve_engine
         // find common headers used in script, will be added to the list
         // of available (predefined) headers (#1489271)
         foreach ($this->script as $rule) {
-            foreach ((array) $rule['tests'] as $test) {
+            foreach ((array) ($rule['tests'] ?? []) as $test) {
                 if ($test['test'] == 'header') {
                     foreach ((array) $test['arg1'] as $header) {
                         $lc_header = strtolower($header);

program/actions/contacts/search.php

@@ -107,7 +107,7 @@ class rcmail_action_contacts_search extends rcmail_action_contacts_index
 
             // check if search fields are supported....
             if (is_array($fields)) {
-                $cols = $source->coltypes[0] ? array_flip($source->coltypes) : $source->coltypes;
+                $cols = !empty($source->coltypes[0]) ? array_flip($source->coltypes) : $source->coltypes;
                 $supported = 0;
 
                 foreach ($fields as $f) {

program/lib/Roundcube/rcube_imap.php

@@ -2441,9 +2441,9 @@ class rcube_imap extends rcube_storage
             $o_part = new rcube_message_part;
             $o_part->ctype_primary   = $part_data['type'];
             $o_part->ctype_secondary = $part_data['subtype'];
-            $o_part->encoding        = $part_data['encoding'];
-            $o_part->charset         = $part_data['charset'];
-            $o_part->size            = $part_data['size'];
+            $o_part->encoding        = $part_data['encoding'] ?? null;
+            $o_part->charset         = $part_data['charset'] ?? null;
+            $o_part->size            = $part_data['size'] ?? null;
         }
 
         $body = '';