Key Select: Fix zeros to work in key selects (#2803)

* fix: csv import to allow 0 items of sample data and field options

* fix: zero key selects to work

Author: squigglybob

dt-posts/posts.php

@@ -2496,7 +2496,7 @@ public static function adjust_post_custom_fields( $post_type, int $post_id, arra
                         }
                     }
                 } elseif ( isset( $field_settings[$key] ) && $field_settings[$key]['type'] == 'key_select' && ( !isset( $field_settings[$key]['private'] ) || !$field_settings[$key]['private'] ) ) {
-                    if ( empty( $value[0]['value'] ) ) {
+                    if ( $value[0]['value'] === '' ) {
                         unset( $fields[$key] );
                         continue;
                     }