MDL-64959 uploaduser: remove leading/trailing spaces from CSV headings

Earlier while uploading users via CSV, if any leading or trailing space was there in
headings of CSV file then error was displayed which will be difficult for a non-technical
person to understand. After this patch, leading and trailing spaces from headings will
be trimmed automatically.

admin/tool/uploaduser/locallib.php

@@ -183,6 +183,7 @@ function uu_validate_user_upload_columns(csv_import_reader $cir, $stdfields, $pr
     $processed = array();
     foreach ($columns as $key=>$unused) {
         $field = $columns[$key];
+        $field = trim($field);
         $lcfield = core_text::strtolower($field);
         if (in_array($field, $stdfields) or in_array($lcfield, $stdfields)) {
             // standard fields are only lowercase