Improve bug74021 test (#17514)

Author: kamil-tekiela

ext/mysqli/tests/bug74021.phpt

@@ -17,7 +17,21 @@ $link->close();
 
 $link = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket);
 $res = $link->query("SELECT RPAD('1',9000000,'1') as a,RPAD('1',9000000,'1') as b");
+if ($res === false) {
+    printf("[001] [%d] %s\n", $link->errno, $link->error);
+}
+
 $r = $res->fetch_array();
+if (!is_array($r)) {
+    printf("[002] Expecting array, got %s/%s\n", gettype($r), $r);
+}
+if(!is_string($r['a'])) {
+    printf("[003] Expecting string, got %s/%s\n", gettype($r['a']), $r['a']);
+}
+if(!is_string($r['b'])) {
+    printf("[004] Expecting string, got %s/%s\n", gettype($r['b']), $r['b']);
+}
+
 var_dump(md5($r['a']));
 var_dump(md5($r['b']));
 ?>