feat: add scrape regex test for useragent string

Author: florianbrinkmann

Diff for: src/Rules/RegexpSpam.php

@@ -111,6 +111,9 @@ public static function verify( array $item ): int {
 			[
 				'rawurl' => '^http[s]?:\/\/(accounts\.)?binance\.com\/[a-zA-Z-]+\/register(-person)?\?ref=[\w]+',
 			],
+			[
+				'useragent' => 'scrape',
+			]
 		];
 
 		$quoted_author = preg_quote( $subject['author'], '/' );
@@ -154,6 +157,10 @@ public static function verify( array $item ): int {
 					continue;
 				}
 
+				if ( ! isset( $subject[ $field ] ) ) {
+					continue;
+				}
+
 				$subject[ $field ] = ( function_exists( 'iconv' ) ? iconv( 'utf-8', 'utf-8//TRANSLIT', $subject[ $field ] ) : $subject[ $field ] );
 
 				if ( empty( $subject[ $field ] ) ) {