prevent iconv decoding from failing

Author: Webklex

src/Header.php

@@ -433,7 +433,7 @@ private function decode(mixed $value): mixed {
  $value = \imap_utf8($value);
  }
  } elseif ($decoder === 'iconv' && $this->is_uft8($value)) {
- $value = iconv_mime_decode($value);
+ $value = iconv_mime_decode($value, ICONV_MIME_DECODE_CONTINUE_ON_ERROR, "UTF-8");
  }
 
  if ($this->is_uft8($value)) {