Authentication milter crashes on incomplete incoming connections with postfix

[dbaldes]

How to reproduce:

• run postfix with authentication milter.
• connect to postfix and immediately disconnect, e.g. using nmap -p 25 -Pn

logs:

postfix/smtpd[25922]: connect from unknown[unknown]
authentication_milter[30163]: Warning: Use of uninitialized value $addr in substr at .../site_perl/5.32.0/Mail/Milter/Authentication/Protocol/Milter.pm line 239.<LF>
authentication_milter[30163]: Unknown IP address format UNDEF
postfix-in/smtpd[25922]: NOQUEUE: lost connection after CONNECT from unknown[unknown]
postfix-in/smtpd[25922]: disconnect from unknown[unknown] commands=0/0
authentication_milter[30163]: NOQUEUE.4778260497D: ERROR: Connect callback error Can't call method "short" on an undefined value at .../site_perl/5.32.0/Mail/Milter/Authentication/Handler.pm line 492.<LF>
authentication_milter[30163]: Child process 30163 shutting down due to fatal error: exit_on_close requested - Exit on close requested<LF>Connect callback error Can't call method "short" on an undefined value at .../site_perl/5.32.0/Mail/Milter/Authentication/Handler.pm line 492.<LF>

Other milters handle this gracefully; see for example cloudmark:

cmfilter[5162]: [T1543501568] ignoring connection from non-INET client