Bug #903046: Fix undefined index error

Change-Id: Ic7dceebfa509f786aebb9dacddbf0836b7e8e1ad
Signed-off-by: Hugh Davenport <hugh@catalyst.net.nz>

htdocs/admin/users/institutions.php

@@ -702,7 +702,7 @@ function institution_submit(Pieform $form, $values) {
 
     // Set the logo after updating the institution, because the institution
     // needs to exist before it can own the logo artefact.
-    if ($values['logo']) {
+    if (!empty($values['logo'])) {
         safe_require('artefact', 'file');
 
         // Entry in artefact table