make common_config() handle nulls correctly

diff --git a/lib/util.php b/lib/util.php
index cd9bd9ed83b421b44e768a6f2e6934d03b2c583f..d1f3bed9e124ddf7a6a4f2caaedc2b40117a4bed 100644 (file)
--- a/lib/util.php
+++ b/lib/util.php
@@ -1152,7 +1152,8 @@ function common_negotiate_type($cprefs, $sprefs)
 function common_config($main, $sub)
 {
     global $config;
-    return isset($config[$main][$sub]) ? $config[$main][$sub] : false;
+    return (array_key_exists($main, $config) &&
+            array_key_exists($sub, $config[$main])) ? $config[$main][$sub] : false;
 }
 
 function common_copy_args($from)