Reset default db_max_allowed_packet, fix max packet size detection

config/defaults.inc.php

@@ -55,7 +55,7 @@ $config['db_table_dsn'] = array(
 // Use them if your server is not MySQL or for better performance.
 // For example Roundcube uses max_allowed_packet value (in bytes)
 // which limits query size for database cache operations.
-$config['db_max_allowed_packet'] = 23423440;
+$config['db_max_allowed_packet'] = null;
 
 
 // ----------------------------------

program/lib/Roundcube/rcube_cache.php

@@ -605,8 +605,10 @@ class rcube_cache
             $this->max_packet = 2097152; // default/max is 2 MB
 
             if ($this->type == 'db') {
-                $value = $this->db->get_variable('max_allowed_packet', $this->max_packet);
-                $this->max_packet = max($value, $this->max_packet) - 2000;
+                if ($value = $this->db->get_variable('max_allowed_packet', $this->max_packet)) {
+                    $this->max_packet = $value;
+                }
+                $this->max_packet -= 2000;
             }
             else if ($this->type == 'memcache') {
                 $stats = $this->db->getStats();

program/lib/Roundcube/rcube_cache_shared.php

@@ -595,8 +595,10 @@ class rcube_cache_shared
             $this->max_packet = 2097152; // default/max is 2 MB
 
             if ($this->type == 'db') {
-                $value = $this->db->get_variable('max_allowed_packet', 1048500);
-                $this->max_packet = min($value, $this->max_packet) - 2000;
+                if ($value = $this->db->get_variable('max_allowed_packet', $this->max_packet)) {
+                    $this->max_packet = $value;
+                }
+                $this->max_packet -= 2000;
             }
             else if ($this->type == 'memcache') {
                 $stats = $this->db->getStats();