fixed bug with possible undefined variable

since the logic statement above uses or, there are times when $has_uri is unset
using (!empty($has_uri)) instead of ($has_uri) prevents PHP throwing an error/warning

fuel/modules/fuel/libraries/Fuel_modules.php

@@ -248,7 +248,7 @@ public function get($module = NULL, $include_advanced = TRUE)
 			$modules = $this->get(NULL, FALSE);
 			foreach($modules as $key => $mod)
 			{
-				if (strtolower($mod->info('model_name')) == $module OR ($has_uri AND $mod->info('module_uri') == $module))
+				if (strtolower($mod->info('model_name')) == $module OR (!empty($has_uri) AND $mod->info('module_uri') == $module))
 				{
 					$module = $key;
 					break;
@@ -1138,4 +1138,4 @@ public function __get($var)
 }
 
 /* End of file Fuel_modules.php */
-/* Location: ./modules/fuel/libraries/fuel/Fuel_modules.php */
+/* Location: ./modules/fuel/libraries/fuel/Fuel_modules.php */