mvc: catch empty data in CSV import

Catch empty lines.  A single "," will generate
an empty string instead of NULL so we are good
here.  It's safe to assume we have at least one
property in the line, otherwise the data is
useless to us anyway.

From the fgetcsv() manual:

A blank line in a CSV file will be returned as an array
comprising a single null field, and will not be treated
as an error.

See: https://www.php.net/manual/en/function.fgetcsv.php

src/opnsense/mvc/app/controllers/OPNsense/Base/ApiMutableModelControllerBase.php

@@ -674,7 +674,7 @@ abstract class ApiMutableModelControllerBase extends ApiControllerBase
         while (($line = fgetcsv($stream, null, $separator)) !== false) {
             if (empty($heading)) {
                 $heading = $line;
-            } else {
+            } elseif (count($line) >= 1 && !is_null($line[0])) {
                 $record = [];
                 foreach ($line as $idx => $content) {
                     if (isset($heading[$idx])) {