Add check that redis_version is set

Author: yatsukhnenko

includes/object-cache.php

@@ -1884,7 +1884,7 @@ protected function lua_flush_closure( $salt, $escape = true ) {
                 return i
 LUA;
 
-            if ( version_compare( $this->redis_version(), '5', '<' ) && version_compare( $this->redis_version(), '3.2', '>=' ) ) {
+            if ( isset($this->redis_version) && version_compare( $this->redis_version, '5', '<' ) && version_compare( $this->redis_version, '3.2', '>=' ) ) {
                 $script = 'redis.replicate_commands()' . "\n" . $script;
             }
 
@@ -1936,7 +1936,7 @@ function ( $group ) {
                 until 0 == cur
                 return i
 LUA;
-            if ( version_compare( $this->redis_version(), '5', '<' ) && version_compare( $this->redis_version(), '3.2', '>=' ) ) {
+            if ( isset($this->redis_version) && version_compare( $this->redis_version, '5', '<' ) && version_compare( $this->redis_version, '3.2', '>=' ) ) {
                 $script = 'redis.replicate_commands()' . "\n" . $script;
             }