Show a friendlier message on init error (#294)

* Show a friendlier message on init error d7a443c

When creating the member extension object in the frontend it needs to
know which section it needs to use as the member info source.

Right now, if the configured value is wrong, you get a weird message
about PHP type checking.

This commit adds a friendlier message when the configuration is not
valid.

* Remove redundant construct 21b320a

Using isset together with !empty is a redundant construct

* Capitalize and pluralize `Members` df4b18c

extension.driver.php

@@ -139,9 +139,12 @@ public function __construct() {
 					else if(isset($members_section_id) && in_array((int)$members_section_id, $config_sections)) {
 						$this->setMembersSection($members_section_id);
 					}
-					else {
+					else if (!empty($config_sections[0])) {
 						$this->setMembersSection($config_sections[0]);
 					}
+					else {
+						throw new Exception(__('No Members section found! Please check your configuration.'));
+					}
 				}
 
 				extension_Members::$initialised = true;