MDL-43896 admin: Avoid empty(expression), not working under PHP 5.4

lib/classes/plugin_manager.php

@@ -294,7 +294,7 @@ class core_plugin_manager {
                 include($fullplug.'/version.php');
 
                 // Check if the legacy $module syntax is still used.
-                if (!is_object($module) or (!empty((array)$module))) {
+                if (!is_object($module) or (count((array)$module) > 0)) {
                     debugging('Unsupported $module syntax detected in version.php of the '.$type.'_'.$plug.' plugin.');
                     $skipcache = true;
                 }

lib/upgradelib.php

@@ -607,7 +607,7 @@ function upgrade_plugins_modules($startcallback, $endcallback, $verbose) {
         require($fullmod .'/version.php');  // Defines $plugin with version etc.
 
         // Check if the legacy $module syntax is still used.
-        if (!is_object($module) or (!empty((array)$module))) {
+        if (!is_object($module) or (count((array)$module) > 0)) {
             throw new plugin_defective_exception($component, 'Unsupported $module syntax detected in version.php');
         }