fallback to "." when gethostname() yield an empty result

ERROR: An empty_argumented EHLO command issued on a machine without hostname

 tmp # date | /usr/bin/mail --debug-level=mailer.prot --exec='set
sendmail=smtps://your_mail:[email protected]' --append='From:
Test <[email protected]>' --subject=Test [email protected]
mail: S: 220 smtp.gmail.com ESMTP l191sm18203421pfc.180 - gsmtp
mail: C: EHLO
mail: S: 501-5.5.4 Empty HELO/EHLO argument not allowed, closing connection.
mail: S: 501 5.5.4  https://support.google.com/mail/?p=helo
l191sm18203421pfc.180 - gsmtp
mail: C: HELO
mail: Cannot open mailer: Input/output error
mail: cannot send message: Input/output error
 tmp #

PATCH to solve this issue:

--- mailutils-3.3/libproto/mailer/smtp_ehlo.c   2017-01-01
13:47:12.000000000 +0000
+++ mailutils-3.3/libproto/mailer/smtp_ehlo.c   2017-01-01
13:47:12.000000000 +0000
@@ -65,6 +65,7 @@
        p++;
       else
        p = host;
+      if(NULL==p||0==p[0]) p=".";
       status = mu_smtp_set_param (smtp, MU_SMTP_PARAM_DOMAIN, p);
       MU_SMTP_CHECK_ERROR (smtp, status);
     }

PATCHED_TEST:
 tmp # date | /usr/bin/mail --debug-level=mailer.prot --exec='set
sendmail=smtps://your_mail:[email protected]
' --append='From: Test <[email protected]>' --subject=Test
[email protected]
mail: S: 220 smtp.gmail.com ESMTP 62sm28074905pfw.129 - gsmtp
mail: C: EHLO .
mail: S: 250-smtp.gmail.com at your service, [106.184.3.179]
...
mail: S: 250 2.0.0 OK 1508465282 62sm28074905pfw.129 - gsmtp
mail: C: QUIT
mail: S: 221 2.0.0 closing connection 62sm28074905pfw.129 - gsmtp

TEST_RESULT:
Received: from . (li1068-179.members.linode.com. [106.184.3.179])
        by smtp.gmail.com with ESMTPSA id
62sm28074905pfw.129.2017.10.19.19.08.00
        for <[email protected]>
        (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256);
        Thu, 19 Oct 2017 19:08:01 -0700 (PDT)
Message-ID: <[email protected]>
...