Fix magento#17582 /bin/magento config:show fails with a fatal error

Author: max-a-mdmitriev

app/code/Magento/Config/Console/Command/ConfigShow/ValueProcessor.php

@@ -97,7 +97,7 @@ public function process($scope, $scopeCode, $value, $path)
         $field = $configStructure->getElementByConfigPath($path);
 
         /** @var Value $backendModel */
-        $backendModel = $field && $field->hasBackendModel()
+        $backendModel = $field && ($field instanceof Field) && $field->hasBackendModel()
             ? $field->getBackendModel()
             : $this->configValueFactory->create();