Only attempt to attach artefacts to blog posts if they were actually created.

Fixes an exception caused by uploading just a leap2a XML file instead of
the zip file. In this case, the leap2a file refers to attachments that
(naturally) aren't included with the upload.
Signed-off-by: Nigel McNie <nigel@catalyst.net.nz>

htdocs/artefact/blog/import/leap/lib.php

@@ -154,7 +154,9 @@ class LeapImportBlog extends LeapImportArtefactPlugin {
                         }
                         $importer->trace("Attaching file $blogpostlink[href] to blog post $blogpostentry->id", PluginImportLeap::LOG_LEVEL_VERBOSE);
                         $artefactids = $importer->get_artefactids_imported_by_entryid((string)$blogpostlink['href']);
-                        $blogpost->attach($artefactids[0]);
+                        if (isset($artefactids[0])) {
+                            $blogpost->attach($artefactids[0]);
+                        }
                     }
                     if ($blogpost) {
                         $blogpost->commit();