Betere foutmelding als import backupfolder niet bestaat (anders kreeg je onduidelijke 'Path not found')

svn path=/Website/branches/v2018.2/; revision=39998

APPL/IMP/imp_shared.js

@@ -425,6 +425,9 @@ function backupfolder(import_app, folder, import_key)
 
     // <folder>\BACKUP<jaar>-<maand>\<import_app>\<fulldate>_<import_key>
     var fso = new ActiveXObject("Scripting.FileSystemObject");
+    if (!fso.FolderExists(folder))
+        throw { description: "Import error: backup folder {0} not found on server".format(folder) };
+
     var jsDate = new Date();
 
     folder = folder.replace("/", "\\");