Fix extract_first_email_addr() to really return the first email

The use of find_all() in extract_email_addrs_vec() extracted occurrences
to an intermediate set and thus lost any sense of ordering.

This changes extract_email_addrs_vec() to use find_all_ordered() and
return all occurrences of email addresses found in the argument,
included duplicates, with their order of occurrence preserved.

testing/external/commit-hash.zeek-testing-private

@@ -1 +1 @@
-8cee05d3405d85a4ae8163d1999b78d182b25213
+c6e8c83cf4d74cde39b57f70a3259cac5a833c1a